These two rows must be in function.php in the theme for the plugin to work: add_theme_support( ‘post-thumbnails’ ); set_post_thumbnail_size( form_option(‘thumbnail_size_w&&echo=false’), form_option(‘thumbnail_size_h&&echo=false’), true ); You’ll also need to add thumbnails to the posts you want visible in the list. After that, all you need to do is to add the hook [categorythumbnaillist 3] (where 3 is a categoy id) to your post.