We report a clinical and histologic study of 70 patients, each with a single melanocytic lesion termed "deep penetrating nevus" (DPN). The lesions are most commonly found on the face, upper trunk, or proximal extremities of patients between the ages of 10 and 30 years. Typically they are darkly pigmented. Histologically they are characterized by loosely organized nests of pleomorphic pigmented cells that penetrate deep into the reticular dermis and often to the subcutaneous fat. Follow-up was obtained from 48 patients. It ranged from 1 to 23 years (mean, 7 years). Despite an initial histologic diagnosis of malignant melanoma in 29% of the cases, there were no local recurrences and no distant metastases. It is important to differentiate DPN from malignant melanoma. The characteristic histologic features of DPN also allow its differentiation from spindle cell and epithelioid cell nevi and blue nevi.