Four percent of 2,446 patients with malignant melanoma did not have a known site of primary origin. More than half were admitted with nodal disease only, and were treated with regional node dissections. Thirty-three percent of this group lived five years, and 22% lived ten years following treatment. One third were admitted with visceral metastases, many of which were amenable to surgery, and this group experienced a 5% five-year survival rate. Cutaneous dissemination carried a lethal prognosis. Recurrences following treatment tended toward the same region of the body as the original metastasis, and 50% of these recurrences occurred within six months of therapy. The sex ratio, age incidence, family history, and survival rates in these patients with unknown primary tumors are consistent with an unnoticed cutaneous lesion as the site of origin for the metastatic disease. It must be supposed that this lesion had undergone spontaneous regression.