Index: src/main/java/org/apache/maven/plugins/site/AbstractSiteMojo.java
===================================================================
--- src/main/java/org/apache/maven/plugins/site/AbstractSiteMojo.java	(revision 607765)
+++ src/main/java/org/apache/maven/plugins/site/AbstractSiteMojo.java	(working copy)
@@ -88,6 +88,16 @@
     protected File siteDirectory;
 
     /**
+     * The root directory of the currently executed project. The whole purpose of this parameter is to retrieve the
+     * relative path to the site directory from the parameter {@link #siteDirectory}, e.g. "src/site".
+     *
+     * @parameter expression="${basedir}"
+     * @required
+     * @readonly
+     */
+    private File baseDirectory;
+
+    /**
      * The maven project.
      *
      * @parameter expression="${project}"
@@ -250,19 +260,33 @@
     /**
      * Get the path of the site descriptor for a given locale.
      *
-     * @param basedir the base dir
+     * @param basedir the base directory of the project whose site descriptor is to retrieve
      * @param locale the locale
      * @return the site descriptor path
      */
     protected File getSiteDescriptorFile( File basedir, Locale locale )
     {
-        String relativePath = getRelativePath( siteDirectory.getAbsolutePath(), basedir.getAbsolutePath() );
+        /*
+         * FIXME: This is a hacky fix for MSITE-91: The location of the site descriptor is best understood as a
+         * project-specific setting and should therefore be configured via a dedicated POM element, e.g.
+         * ${project.reporting.siteDirectory}, that the super POM defaults to "src/site". Specifying the site directory
+         * in the plugin configuration raises the following problem for the plugin: When the site descriptors for parent
+         * projects need to be retrieved, where should the plugin look? The plugin only knows about the site directory
+         * of the currently executed sub project but ancestor projects may use a different location for their site.xml.
+         * For now, we assume that all ancestor projects from which the current project inherits use the same location
+         * for the site.xml (relative to their base directories). When this architectural design flaw gets hopefully
+         * fixed in Maven 2.1, the signature of this method should be changed to ( MavenProject, Locale ) such that the
+         * site directory can be retrieved from the desired POM. The mojo parameters siteDirectory and baseDirectory
+         * should be deleted then.
+         */
+        String relativePath = getRelativePath( siteDirectory.getAbsolutePath(), baseDirectory.getAbsolutePath() );
+        File siteDir = new File( basedir, relativePath );
 
-        File siteDescriptor = new File( relativePath, "site_" + locale.getLanguage() + ".xml" );
+        File siteDescriptor = new File( siteDir, "site_" + locale.getLanguage() + ".xml" );
 
         if ( !siteDescriptor.exists() )
         {
-            siteDescriptor = new File( relativePath, "site.xml" );
+            siteDescriptor = new File( siteDir, "site.xml" );
         }
         return siteDescriptor;
     }
@@ -789,8 +813,13 @@
             {
                 try
                 {
+                    String relativePath = aProject.getModel().getParent().getRelativePath();
+                    if ( new File( relativePath ).isDirectory() )
+                    {
+                        relativePath = new File( relativePath, "pom.xml" ).getPath();
+                    }
                     MavenProject mavenProject = mavenProjectBuilder.build(
-                        new File( aProject.getBasedir(), aProject.getModel().getParent().getRelativePath() ),
+                        new File( aProject.getBasedir(), relativePath ),
                         localRepository, null );
                     if ( mavenProject.getGroupId().equals( origParent.getGroupId() )
                         && mavenProject.getArtifactId().equals( origParent.getArtifactId() )