Of 226 consecutive papillary carcinoma patients, 14 indicated that at least one other relative was similarly affected. Pathology confirmation was obtained in 8 of the 14 families. Of the eight families with documented familial papillary carcinoma, one had five members, another had four members, and yet another had three members affected. The remaining families had two members affected. In those families with two or more persons with confirmed papillary carcinomas of the thyroid, 20 first- and second-degree relatives were examined. Of those, one had a previously unidentified papillary carcinoma and 6 had a benign thyroid disease (4 primary hypothyroidism and 2 simple goiters). High-resolution chromosome studies of four patients from four different families were normal, and there was no increase in chromosome breakage in a fifth patient from yet another family. Autosomal dominant inheritance is possible. Although there was no family history of lipomas, osteomas, or intestinal polyposis to suggest Gardner syndrome, four parents of our familial papillary carcinoma patients had colon cancer. In addition, three other relatives died of unidentified intra-abdominal cancer. The apparently high frequency of colon cancer and other abdominal cancer in relatives was an additional concern. Based on our observations, three clinical recommendations can be made: obtain a family history of all patients with papillary carcinoma of the thyroid, since between 3.5 to 6.2% will have another affected relative; when two or more persons in a family have papillary carcinoma of the thyroid, all first- and second-degree relatives should have a neck palpation by an experienced examiner; and families with two or more persons with papillary carcinoma should be observed for possible colon cancer.