WordPress Related Posts by Category

related_posts.php

<?php
// related posts by category
$related = get_posts( array( 'category__in' => wp_get_post_categories($post->ID), 'numberposts' => 2, 'orderby' => 'rand', 'post__not_in' => array($post->ID) ) );
if($related): 
foreach($related as $post):
setup_postdata($post); 
?>
    <ul>
        <li>
        <a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a>
        </li>
    </ul>
<?php 
endforeach;
wp_reset_postdata(); 
endif;