<?php
$test = "";
$posttags = get_the_tags();
if ($posttags) {
foreach($posttags as $tag) {
    $test .= ',' . $tag->name;
}
}
$test = substr($test, 1);
query_posts('tag=' .$test . '&showposts=-1'); while (have_posts()) : the_post(); ?>
      <li><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></li>
<?php endwhile; wp_reset_query(); ?>