&NA;Familial adenomatous polyposis was always believed to be a colonic disease of genetic determination with a high risk of development of cancer of the large bowel. Over the years the list of extracolonic manifestations of this disease, both benign and malignant, has amplified. Brain tumors and, in particular, medulloblastoma have not become recognized as major malignant extracolonic manifestations of familial adenomatous polyposis. They are of particular significance because, unlike most of the other manifestations, they occur prior to or early in the development of the colonic manifestations of this disease. This report documents the investigation of 168 kindreds in The Cleveland Clinic Familial Adenomatous Polyposis Registry in a search for those at‐risk individuals who developed brain tumors.