Primary malignant melanoma is only rarely found in the oral cavity (estimated at between 0.2 and 8 per cent of all melanomas) and occurs approximately four times more frequently in the oral mucosa of the upper jaw, usually on the palate or alveolar gingivae. A case is reported of a malignant melanoma in the mouth of a 74 year old male, which was originally diagnosed as reactive denture hyperplasia caused by a ill-fitting upper denture. Correction of the denture fault failed to stop the growth of the mass, which was therefore removed surgically. Histological examination revealed a melanin-producing tumour. A partial maxillectomy was performed and there was no evidence of recurrence over a three year follow-up period.