We review five cases in which CT demonstrated severe unilateral atrophy of the latissimus dorsi muscle. In four of these cases, similar findings were also seen in the inferior portion of the serratus anterior muscle. All patients had undergone thoracic surgery on the ipsilateral side 10 months to 3 1/2 years prior to CT. All patients had undergone posterolateral thoracotomy, including one who had undergone successive right and left posterolateral thoracotomies. The most likely explanation for the CT finding of atrophy is denervation injury resulting from surgical incision. We discuss normal innervation of the posterolateral chest wall musculature, with emphasis on the relationship of unilateral atrophy of posterolateral chest wall musculature to previous surgical incision.