Beckwith-Wiedemann syndrome, familial atypical multiple mole melanoma syndrome, and hereditary tylosis are bona fide genodermatoses with malignant potential. Each of these conditions is associated with an increased incidence of certain tumors: Wilms' tumor, adrenocortical carcinomas, pancreatoblastomas, and hepatoblastomas in Beckwith-Wiedemann syndrome; intraocular malignant melanoma, pancreatic carcinoma, and noncolorectal gastrointestinal cancers in familial atypical multiple mole melanoma syndrome; and squamous cell carcinoma of the esophagus in hereditary tylosis. Other cancer-related genodermatoses are Birt-Hogg-Dube syndrome (associated with medullary carcinoma of the thyroid and renal cell carcinoma) and its variant, Hornstein-Knickenberg syndrome (associated with colon carcinoma). Kidney tumors (Wilms' tumor and malignant rhabdoid tumor), leukemias (acute myelogenous and acute myelomonocytic), retinoblastoma, and paratesticular rhabdomyosarcoma have been reported recently in children with another genodermatosis-incontinentia pigmenti. Supernumerary nipples (polythelia) may be sporadic or familial in occurrence; their presence has been associated with an increased incidence of renal adenocarcinoma, testicular cancer, prostate cancer, and urinary bladder carcinoma. The general characteristics, mucosal and skin manifestations, and noncutaneous features of all these conditions are reviewed. Also, the associated malignancies of these genodermatoses and other conditions that are characterized by dermatologic manifestations and may be either familial or secondary to an inherited gene defect are summarized.