In a sibship of nine, six members had hereditary medullary carcinoma of the thyroid. Two of those with thyroid neoplasms and two without had numerous small papular skin lesions. These proved to be a type of pilar tumor that we named fibrofolliculoma. Further investigation of the total kindred of 70 showed no other evidence of thyroid neoplasm. Skin tumors only appeared after the age of 25 years. Fifteen of 37 members older than the age of 25 years exhibited the typical skin lesions. Obviously, the original sibship was the repository of two dominantly inherited traits. The fibrofolliculoma is characterized by abnormal hair follicles with epithelial strands extending out from the infundibulum of the hair follicle into a hyperplastic mantle of specialized firbrous tissue. Associated skin lesions in this kindred were trichodiscomas and acrochordons.