Index: wp-includes/nav-menu-template.php
===================================================================
--- wp-includes/nav-menu-template.php	(revision 15277)
+++ wp-includes/nav-menu-template.php	(working copy)
@@ -75,7 +75,7 @@
 		$class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );
 		$class_names = ' class="' . esc_attr( $class_names ) . '"';
 
-		$output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $value . $class_names .'>';
+		$output .= $indent . '<li id="' . apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args ) . '"' . $value . $class_names .'>';
 
 		$attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
 		$attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';