A clinico-pathologic study on 12 patients with subungual malignant melanoma (SUM) is presented and cases from the literature are reviewed. The difficult diagnosis of SUM as well as the differential diagnosis is discussed. The SUM sometimes called "melanotic whitlow", is often misdiagnosed and therefore may worsen the prognosis. Every persistent nail disorder which does not respond to treatment should rise suspicion of SUM, especially if not pigmented.