Melanoma is an important human cancer, the etiology of which has been the subject of much study. Recently a gene for familial melanoma, MLM, has been mapped and isolated. This gene encodes the cell-cycle regulator p16 and is mutated in a variety of sporadic human cancers in addition to melanoma. The isolation of MLM answers some questions in the area of melanoma biology, but raises others. Identification of p16 and other genes that contribute to melanoma development may be viewed as one step in the attempt to understand, diagnose, and treat this malignant disease.