Fifteen cases of malignant melanoma occurring in two or more family members were found among the family histories of 250 hospital records selected for review. This familial incidence far exceeds that expected by chance alone. Each instance of melanoma was histologically verified, and current pedigrees on each family were obtained. The clinical onset of melanoma in these and other reported familial cases tended to occur at an earlier age in successive generations and at a similar age in siblings. The occurrence of melanoma in families suggests a genetic predisposition to the development of this cancer, although the mode of inheritance cannot presently be defined. Observation of relatives of patients with melanoma may lead to earlier detection of this malignancy.