Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 20163)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -577,6 +577,10 @@
 			'sticky'            => ( $post['post_type'] === 'post' && is_sticky( $post['ID'] ) ),
 		);
 
+		//
+		$post_fields['featured_image']     = get_post_meta( $post['ID'], '_thumbnail_id', true );
+		$post_fields['featured_image_url'] = wp_get_attachment_url( $post_fields['featured_image'] );
+
 		// Consider future posts as published
 		if ( $post_fields['post_status'] === 'future' )
 			$post_fields['post_status'] = 'publish';
@@ -644,6 +648,7 @@
 	 *      - comment_status - can be 'open' | 'closed'
 	 *      - ping_status - can be 'open' | 'closed'
 	 *      - sticky
+	 *      - featured_image - ID of a media item to use as the featured image
 	 *      - custom_fields - array, with each element containing 'key' and 'value'
 	 *      - terms - array, with taxonomy names as keys and arrays of term IDs as values
 	 *      - terms_names - array, with taxonomy names as keys and arrays of term names as values
@@ -777,6 +782,18 @@
 			stick_post( $post_ID );
 		}
 
+		if ( isset ( $post_data['featured_image'] ) ) {
+			// empty value deletes, non-empty value adds/updates
+			if ( empty( $post_data['featured_image'] ) ) {
+				delete_post_thumbnail( $post_ID );
+			}
+			else {
+				if ( set_post_thumbnail( $post_ID, $post_data['featured_image'] ) === false )
+					return new IXR_Error( 404, __( 'Invalid attachment ID.' ) );
+			}
+			unset( $content_struct['featured_image'] );
+		}
+
 		if ( isset ( $post_data['custom_fields'] ) && post_type_supports( $post_data['post_type'], 'custom-fields' ) ) {
 			$this->set_custom_fields( $post_ID, $post_data['custom_fields'] );
 		}
@@ -3329,6 +3346,7 @@
 	 *  - mt_allow_pings - can be 'open' or 'closed'
 	 *  - date_created_gmt
 	 *  - dateCreated
+	 *  - wp_featured_image
 	 *
 	 * @since 1.5.0
 	 *
@@ -3575,6 +3593,13 @@
 		if ( isset($content_struct['custom_fields']) )
 			$this->set_custom_fields($post_ID, $content_struct['custom_fields']);
 
+		if ( isset ( $post_data['wp_featured_image'] ) ) {
+			if ( set_post_thumbnail( $post_ID, $post_data['wp_featured_image'] ) === false )
+				return new IXR_Error( 404, __( 'Invalid attachment ID.' ) );
+
+			unset( $content_struct['wp_featured_image'] );
+		}
+
 		// Handle enclosures
 		$thisEnclosure = isset($content_struct['enclosure']) ? $content_struct['enclosure'] : null;
 		$this->add_enclosure_if_new($post_ID, $thisEnclosure);
@@ -3875,6 +3900,18 @@
 		if ( isset($content_struct['custom_fields']) )
 			$this->set_custom_fields($post_ID, $content_struct['custom_fields']);
 
+		if ( isset ( $post_data['wp_featured_image'] ) ) {
+			// empty value deletes, non-empty value adds/updates
+			if ( empty( $post_data['wp_featured_image'] ) ) {
+				delete_post_thumbnail( $post_ID );
+			}
+			else {
+				if ( set_post_thumbnail( $post_ID, $post_data['wp_featured_image'] ) === false )
+					return new IXR_Error( 404, __( 'Invalid attachment ID.' ) );
+			}
+			unset( $content_struct['wp_featured_image'] );
+		}
+
 		// Handle enclosures
 		$thisEnclosure = isset($content_struct['enclosure']) ? $content_struct['enclosure'] : null;
 		$this->add_enclosure_if_new($post_ID, $thisEnclosure);
@@ -4011,6 +4048,9 @@
 
 			if ( !empty($enclosure) ) $resp['enclosure'] = $enclosure;
 
+			$resp['wp_featured_image'] = get_post_meta( $postdata['ID'], '_thumbnail_id', true );
+			$resp['wp_featured_image_url'] = wp_get_attachment_url( $resp['wp_featured_image'] );
+
 			return $resp;
 		} else {
 			return new IXR_Error(404, __('Sorry, no such post.'));
@@ -4125,6 +4165,9 @@
 				'date_modified_gmt' => new IXR_Date( $post_modified_gmt )
 			);
 
+			$entry_index = count( $struct ) - 1;
+			$struct[ $entry_index ][ 'wp_featured_image' ]     = get_post_meta( $entry['ID'], '_thumbnail_id', true );
+			$struct[ $entry_index ][ 'wp_featured_image_url' ] = wp_get_attachment_url( $struct[ $entry_index ][ 'wp_featured_image' ] );
 		}
 
 		$recent_posts = array();