diff --git modules/field/tests/field.test modules/field/tests/field.test
index ee6351e..c5bf315 100644
--- modules/field/tests/field.test
+++ modules/field/tests/field.test
@@ -988,11 +988,12 @@ class FieldInfoTestCase extends FieldTestCase {
    */
   function testFieldInfo() {
     // Test that field_test module's fields, widgets, and formatters show up.
-    $field_test_info = field_test_field_info();
-    $formatter_info = field_test_field_formatter_info();
-    $widget_info = field_test_field_widget_info();
-    $storage_info = field_test_field_storage_info();
 
+    $field_test_info = field_test_field_info();
+    // We need to account for the existence of user_field_info_alter().
+    foreach (array_keys($field_test_info) as $name) {
+      $field_test_info[$name]['instance_settings']['user_register_form'] = FALSE;
+    }
     $info = field_info_field_types();
     foreach ($field_test_info as $t_key => $field_type) {
       foreach ($field_type as $key => $val) {
@@ -1001,6 +1002,7 @@ class FieldInfoTestCase extends FieldTestCase {
       $this->assertEqual($info[$t_key]['module'], 'field_test',  t("Field type field_test module appears"));
     }
 
+    $formatter_info = field_test_field_formatter_info();
     $info = field_info_formatter_types();
     foreach ($formatter_info as $f_key => $formatter) {
       foreach ($formatter as $key => $val) {
@@ -1009,6 +1011,7 @@ class FieldInfoTestCase extends FieldTestCase {
       $this->assertEqual($info[$f_key]['module'], 'field_test',  t("Formatter type field_test module appears"));
     }
 
+    $widget_info = field_test_field_widget_info();
     $info = field_info_widget_types();
     foreach ($widget_info as $w_key => $widget) {
       foreach ($widget as $key => $val) {
@@ -1017,6 +1020,7 @@ class FieldInfoTestCase extends FieldTestCase {
       $this->assertEqual($info[$w_key]['module'], 'field_test',  t("Widget type field_test module appears"));
     }
 
+    $storage_info = field_test_field_storage_info();
     $info = field_info_storage_types();
     foreach ($storage_info as $s_key => $storage) {
       foreach ($storage as $key => $val) {
@@ -1180,6 +1184,10 @@ class FieldInfoTestCase extends FieldTestCase {
    */
   function testSettingsInfo() {
     $info = field_test_field_info();
+    // We need to account for the existence of user_field_info_alter().
+    foreach (array_keys($info) as $name) {
+      $info[$name]['instance_settings']['user_register_form'] = FALSE;
+    }
     foreach ($info as $type => $data) {
       $this->assertIdentical(field_info_field_settings($type), $data['settings'], "field_info_field_settings returns {$type}'s field settings");
       $this->assertIdentical(field_info_instance_settings($type), $data['instance_settings'], "field_info_field_settings returns {$type}'s field instance settings");
diff --git modules/field_ui/field_ui.admin.inc modules/field_ui/field_ui.admin.inc
index 33924f7..8836a95 100644
--- modules/field_ui/field_ui.admin.inc
+++ modules/field_ui/field_ui.admin.inc
@@ -1731,6 +1731,7 @@ function field_ui_field_edit_form($form, &$form_state, $instance) {
   drupal_set_title($instance['label']);
 
   $form['#field'] = $field;
+  $form['#instance'] = $instance;
 
   if (!empty($field['locked'])) {
     $form['locked'] = array(
diff --git modules/user/user.js modules/user/user.js
index 1336d44..3d884ce 100644
--- modules/user/user.js
+++ modules/user/user.js
@@ -173,4 +173,25 @@ Drupal.evaluatePasswordStrength = function (password, translate) {
 
 };
 
+/**
+ * Field instance settings screen: force the 'Display on registration form'
+ * checkbox checked whenever 'Required' is checked.
+ */
+Drupal.behaviors.fieldUserRegistration = {
+  attach: function (context, settings) {
+    var $checkbox = $('form#field-ui-field-edit-form input#edit-instance-settings-user-register-form');
+
+    if ($checkbox.size()) {
+      $('input#edit-instance-required', context).once('user-register-form-checkbox', function () {
+        $(this).bind('change', function (e) {
+          if ($(this).attr('checked')) {
+            $checkbox.attr('checked', true);
+          }
+        });
+      });
+
+    }
+  }
+};
+
 })(jQuery);
diff --git modules/user/user.module modules/user/user.module
index da80733..ff47abf 100644
--- modules/user/user.module
+++ modules/user/user.module
@@ -177,6 +177,18 @@ function user_uri($user) {
 }
 
 /**
+ * Implements hook_field_info_alter().
+ */
+function user_field_info_alter(&$info) {
+  // Add the 'user_register_form' instance setting to all field types.
+  foreach ($info as $field_type => $field_type_info) {
+    $info[$field_type]['instance_settings'] += array(
+      'user_register_form' => FALSE,
+    );
+  }
+}
+
+/**
  * Implements hook_field_extra_fields().
  */
 function user_field_extra_fields() {
@@ -3520,6 +3532,55 @@ function user_block_user_action(&$entity, $context = array()) {
 }
 
 /**
+ * Implements hook_form_FORM_ID_alter().
+ *
+ * Add a checkbox for the 'user_register_form' instance settings on the 'Edit
+ * field instance' form.
+ */
+function user_form_field_ui_field_edit_form_alter(&$form, &$form_state, $form_id) {
+  $instance = $form['#instance'];
+
+  if ($instance['entity_type'] == 'user') {
+    $form['instance']['settings']['user_register_form'] = array(
+      '#type' => 'checkbox',
+      '#title' => t('Display on user registration form.'),
+      '#description' => t("This is compulsory for 'required' fields."),
+      // Field instances created in D7 beta releases before the setting was
+      // introduced might be set as 'required' and 'not shown on user_register
+      // form'. We make sure the checkbox comes as 'checked' for those.
+      '#default_value' => $instance['settings']['user_register_form'] || $instance['required'],
+      // Display just below the 'required' checkbox.
+      '#weight' => $form['instance']['required']['#weight'] + .1,
+      // Disabled when the 'required' checkbox is checked.
+      '#states' => array(
+        'enabled' => array('input[name="instance[required]"]' => array('checked' => FALSE)),
+      ),
+      // Checked when the 'required' checkbox is checked. This is done through
+      // a custom behavior, since the #states system would also synchronize on
+      // uncheck.
+      '#attached' => array(
+        'js' => array(drupal_get_path('module', 'user') . '/user.js'),
+      ),
+    );
+
+    array_unshift($form['#submit'], 'user_form_field_ui_field_edit_form_submit');
+  }
+}
+
+/**
+ * Additional submit handler for the 'Edit field instance' form.
+ *
+ * Make sure the 'user_register_form' setting is set for required fields.
+ */
+function user_form_field_ui_field_edit_form_submit($form, &$form_state) {
+  $instance = $form_state['values']['instance'];
+
+  if (!empty($instance['required'])) {
+    form_set_value($form['instance']['settings']['user_register_form'], 1, $form_state);
+  }
+}
+
+/**
  * Form builder; the user registration form.
  *
  * @ingroup forms
@@ -3546,6 +3607,15 @@ function user_register_form($form, &$form_state) {
   // Start with the default user account fields.
   user_account_form($form, $form_state);
 
+  // Attach field widgets, and hide the ones where the 'user_register_form'
+  // setting is not on.
+  field_attach_form('user', $form['#user'], $form, $form_state);
+  foreach (field_info_instances('user', 'user') as $field_name => $instance) {
+    if (empty($instance['settings']['user_register_form'])) {
+      $form[$field_name]['#access'] = FALSE;
+    }
+  }
+
   if ($admin) {
     // Redirect back to page which initiated the create request;
     // usually admin/people/create.
@@ -3558,6 +3628,7 @@ function user_register_form($form, &$form_state) {
     '#value' => t('Create new account'),
   );
 
+  $form['#validate'][] = 'user_register_validate';
   // Add the final user registration form submit handler.
   $form['#submit'][] = 'user_register_submit';
 
@@ -3565,6 +3636,13 @@ function user_register_form($form, &$form_state) {
 }
 
 /**
+ * Validation function for the user registration form.
+ */
+function user_register_validate($form, &$form_state) {
+  entity_form_field_validate('user', $form, $form_state);
+}
+
+/**
  * Submit handler for the user registration form.
  *
  * This function is shared by the installation form and the normal registration form,
@@ -3583,13 +3661,21 @@ function user_register_submit($form, &$form_state) {
   }
   $notify = !empty($form_state['values']['notify']);
 
+  // Remove unneeded values.
   form_state_values_clean($form_state);
 
   $form_state['values']['pass'] = $pass;
   $form_state['values']['init'] = $form_state['values']['mail'];
 
   $account = $form['#user'];
-  $account = user_save($account, $form_state['values']);
+
+  entity_form_submit_build_entity('user', $account, $form, $form_state);
+
+  // Populate $edit with the properties of $account, which have been edited on
+  // this form by taking over all values, which appear in the form values too.
+  $edit = array_intersect_key((array) $account, $form_state['values']);
+  $account = user_save($account, $edit);
+
   // Terminate if an error occurred during user_save().
   if (!$account) {
     drupal_set_message(t("Error saving user account."), 'error');
diff --git modules/user/user.test modules/user/user.test
index a7925ca..977f5a3 100644
--- modules/user/user.test
+++ modules/user/user.test
@@ -10,6 +10,10 @@ class UserRegistrationTestCase extends DrupalWebTestCase {
     );
   }
 
+  function setUp() {
+    parent::setUp('field_test');
+  }
+
   function testRegistrationWithEmailVerification() {
     // Require e-mail verification.
     variable_set('user_email_verification', TRUE);
@@ -137,6 +141,91 @@ class UserRegistrationTestCase extends DrupalWebTestCase {
     $this->assertEqual($new_user->picture, '', t('Correct picture field.'));
     $this->assertEqual($new_user->init, $mail, t('Correct init field.'));
   }
+
+  /**
+   * Tests Field API fields on user registration forms.
+   */
+  function testRegistrationWithUserFields() {
+    // Create a field, and an instance on 'user' entity type.
+    $field = array(
+      'type' => 'test_field',
+      'field_name' => 'test_user_field',
+      'cardinality' => 1,
+    );
+    field_create_field($field);
+    $instance = array(
+      'field_name' => 'test_user_field',
+      'entity_type' => 'user',
+      'label' => 'Some user field',
+      'bundle' => 'user',
+      'required' => TRUE,
+      'settings' => array('user_register_form' => FALSE),
+    );
+    field_create_instance($instance);
+
+    // Check that the field does not appear on the registration form.
+    $this->drupalGet('user/register');
+    $this->assertNoText($instance['label'], t('The field does not appear on user registration form'));
+
+    // Have the field appear on the registration form.
+    $instance['settings']['user_register_form'] = TRUE;
+    field_update_instance($instance);
+    $this->drupalGet('user/register');
+    $this->assertText($instance['label'], t('The field appears on user registration form'));
+
+    // Check that validation errors are correctly reported.
+    $edit = array();
+    $edit['name'] = $name = $this->randomName();
+    $edit['mail'] = $mail = $edit['name'] . '@example.com';
+    // Missing input in required field.
+    $edit['test_user_field[und][0][value]'] = '';
+    $this->drupalPost(NULL, $edit, t('Create new account'));
+    $this->assertRaw(t('@name field is required.', array('@name' => $instance['label'])), t('Field validation error was correctly reported.'));
+    // Invalid input.
+    $edit['test_user_field[und][0][value]'] = '-1';
+    $this->drupalPost(NULL, $edit, t('Create new account'));
+    $this->assertRaw(t('%name does not accept the value -1.', array('%name' => $instance['label'])), t('Field validation error was correctly reported.'));
+
+    // Submit with valid data.
+    $value = rand(1, 255);
+    $edit['test_user_field[und][0][value]'] = $value;
+    $this->drupalPost(NULL, $edit, t('Create new account'));
+    // Check user fields.
+    $accounts = user_load_multiple(array(), array('name' => $name, 'mail' => $mail));
+    $new_user = reset($accounts);
+    $this->assertEqual($new_user->test_user_field[LANGUAGE_NONE][0]['value'], $value, t('The field value was correclty saved.'));
+
+    // Check that the 'add more' button works.
+    $field['cardinality'] = FIELD_CARDINALITY_UNLIMITED;
+    field_update_field($field);
+    foreach (array('js', 'nojs') as $js) {
+      $this->drupalGet('user/register');
+      // Add two inputs.
+      $value = rand(1, 255);
+      $edit = array();
+      $edit['test_user_field[und][0][value]'] = $value;
+      if ($js == 'js') {
+        $this->drupalPostAJAX(NULL, $edit, 'test_user_field_add_more');
+        $this->drupalPostAJAX(NULL, $edit, 'test_user_field_add_more');
+      }
+      else {
+        $this->drupalPost(NULL, $edit, t('Add another item'));
+        $this->drupalPost(NULL, $edit, t('Add another item'));
+      }
+      // Submit with three values.
+      $edit['test_user_field[und][1][value]'] = $value + 1;
+      $edit['test_user_field[und][2][value]'] = $value + 2;
+      $edit['name'] = $name = $this->randomName();
+      $edit['mail'] = $mail = $edit['name'] . '@example.com';
+      $this->drupalPost(NULL, $edit, t('Create new account'));
+      // Check user fields.
+      $accounts = user_load_multiple(array(), array('name' => $name, 'mail' => $mail));
+      $new_user = reset($accounts);
+      $this->assertEqual($new_user->test_user_field[LANGUAGE_NONE][0]['value'], $value, t('@js : The field value was correclty saved.', array('@js' => $js)));
+      $this->assertEqual($new_user->test_user_field[LANGUAGE_NONE][1]['value'], $value + 1, t('@js : The field value was correclty saved.', array('@js' => $js)));
+      $this->assertEqual($new_user->test_user_field[LANGUAGE_NONE][2]['value'], $value + 2, t('@js : The field value was correclty saved.', array('@js' => $js)));
+    }
+  }
 }
 
 class UserValidationTestCase extends DrupalWebTestCase {