<?php							
	$catArray = explode("</li>",wp_list_categories('title_li=&echo=0&depth=1'));
	$catCount = count($catArray) - 1;
	$catColumns = round($catCount / 3);
	$twoColumns = round($catColumns + $catColumns);
 
	for ($i=0;$i<$catCount;$i++) {
		if ($i<$catColumns){
			$catLeft = $catLeft.''.$catArray[$i].'</li>';
	         }
		elseif ($i<$twoColumns) {
			$catMiddle = $catMiddle.''.$catArray[$i].'</li>';
		} 
		elseif ($i>=$catColumns){
			$catRight = $catRight.''.$catArray[$i].'</li>';
		 }  
	};
?>
 
<ul class="left">
      <?php echo $catLeft; ?>
</ul>
<ul class="middle">
	<?php echo $catMiddle; ?>
</ul>
<ul class="right">
      <?php echo $catRight; ?>
</ul>