Primary malignant melanoma occurring in mucous membranes is uncommon. Of 410 patients with malignant melanoma, 14 (3.4%) had their primary tumour located in mucosal membranes. Five of the tumours were in the mucosal lining of the head and neck, five in the gastrointestinal tract mucosa and four in the female genitalia. Eight of the tumours were ulcerated, necrotic and deeply invasive. The most common histological subtype was acral lentiginous melanoma. Surgical resection of the primary tumour was performed in 10 patients. In the other four, surgery was not feasible, and they were treated by irradiation and immunotherapy. Six patients underwent regional lymph node dissection. In four of them, regional metastases were found. Chemotherapy was given to seven patients for widespread metastases. Nine patients (64%) died of metastatic melanoma within 2 years. The remaining five patients are alive after 3 to 8 years. It appears that mucosal membrane melanoma is a distinct variant of the disease due to both its aggressive biological behaviour and its relative inaccessibility for surgical removal, and may therefore be classified separately.