High resolution ultrasound (HRUS) was tested in 58 cutaneous malignant melanomas to check its validity in evaluating tumor thickness in vivo before surgery. The values obtained with this method were compared with histologic values (measured according to Breslow); a highly significant correlation was found (r = 0.895, p less than 0.001). The accuracy of HRUS in distinguishing between low- and high-risk cutaneous malignant melanoma was also found to be quite high. Our data therefore justify the use of such a technique in the preoperative staging procedure.