diff --git a/term_reference_tree.api.php b/term_reference_tree.api.php
new file mode 100644
index 0000000..3f42a2d
--- /dev/null
+++ b/term_reference_tree.api.php
@@ -0,0 +1,38 @@
+<?php
+/**
+ * @files
+ * Documentation for hooks defined in term_reference_tree project
+ */
+
+/**
+ * Hook to allow the form elements of a tree to be modified by other code.
+ *
+ * @param array $element
+ *   The checkbox/radio button element for a single term.
+ * @param array $context
+ *   An array with the following keys:
+ *     'element' => Array of the main checkbox_tree element.
+ *     'term' => A taxonomy term object.  $term->children should be an array of the term
+ *               objects that are that term's children.
+ *     'form_state' => The form state array.
+ */
+function hook_term_reference_tree_element_alter( &$element, $context ) {
+  global $user; // Used by example below.
+
+  // Some examples of info that can be found in the context
+  $form_id = $context['form_state']['build_info']['form_id'];
+  $vocab_obj = $context['element']['#vocabulary'];
+  $field_name = $context['element']['#field_name'];
+  $term = $context['term'];
+
+  // Example of disabling some of the terms in the tree.
+  if ( $field_name = "field_my_tags" ) {
+    // Call some custom code to get user specific tags to disable.
+    // Returns an array of tids.
+    $disabled = my_module_get_disabled_tags( $user );
+    if ( in_array($term->tid, $disabled ) ) {
+      $element['#disabled'] = TRUE;
+    }
+  }
+}
+
diff --git a/term_reference_tree.widget.inc b/term_reference_tree.widget.inc
index 1685a43..3a5f9dc 100644
--- a/term_reference_tree.widget.inc
+++ b/term_reference_tree.widget.inc
@@ -705,6 +705,12 @@ function _term_reference_tree_build_item($element, $term, $form_state, $value, $
       $e['#id'] = drupal_html_id('edit-' . implode('-', $parents_for_id));
       $e['#parents'] = $element['#parents'];
     }
+    $context = array(
+      'element' => $element,
+      'term' => $term,
+      'form_state' => $form_state,
+    );
+    drupal_alter('term_reference_tree_element', $e, $context) ;
   }
   else {
     $e = array(