Two cases of melanoma of the skin, occurring in a brother and sister of the same family, are presented. A pigmented lesion was removed from the neck of a 54-year-old man five years after a surgeon first advised removal. The patient is without recurrence three years after the lesion was excised. Microscopically the lesion proved to be malignant melanoma. A sister, age 34, had been treated 11 years earlier for a tumor that appeared after trauma to the left thigh. Four years previously a "mole" had been removed from this site. She died of malignant melanoma in August 1953. Several earlier reports of familial occurrences of this disease are cited that suggest genetic factors are important in the determination of this relatively rare condition. These cases appear to support this view.