A kindred contained at least 10 members with single or multiple juvenile polyps of the stomach and large intestine. Several additional polyps had both adenomatous and juvenile features. Eleven members of the kindred have had gastrointestinal carcinoma of the stomach, duodenum, pancreas, or proximal colon. The pattern of inheritance in this kindred suggests either a single or two closely linked autosomal dominant determinants for gastrointestinal carcinoma and polyposis. Management of this kindred is complicated due to the occurrence of gastrointestinal carcinoma without polyposis.