A hundred and fifteen skin tumors were evaluated by means of US. Three variables were considered for each lesion--i.e., borders, echostructure and thickness--and the results compared with histology. High agreement was observed in melanomas: in these tumors, indeed, thickness is well known to be relevant for both surgical planning and prognosis. US scans with a 10 MHz transducer allowed the accurate assessment of borders and structure only in certain, mainly benign, kinds of skin tumors--e.g., angiomas, pilomatrixomas, sebaceous cysts and lipomas--, but also in lymphomas. On the contrary, most malignant neoplasms exhibit hypoechoic structure and borders from clear-cut to blurred. Finally, US proved to be highly reliable in demonstrating lesion thickness before surgery. High agreement was once again observed with histology relative to this variable: thickness (in mm) was the same in 30% of cases, overestimated by US (mean: 0.3 mm) in 44% of cases and underestimated by US (mean: 0.15 mm) in 26% of cases. Particularly, in 41 melanomas, histology-US agreement rate was 44% for the Breslow index, with r = 0.95 and 88% for the Clark index.