The clinical and histopathologic characteristics of gastric carcinoma in young patients (less than 40 years old) were studied retrospectively. The carcinoma was of the diffuse type in 94% of the young patients, and typical features were poor prognosis, an equal sex ratio, and a strong association with blood group A. The family histories of the young patients were studied. There was a highly significant (p less than 0.001) overrepresentation of gastric cancer in the parents of the index cases. In four instances (13%) the findings were compatible with hereditary cancer. One of the patients belonged to a cancer family syndrome (CFS) kindred. The CFS is an autosomal, dominantly inherited trait for adenocarcinomas is well documented. It seems, on the basis of the present study, that CFS should also be added to the list of genetic risk factors for gastric carcinoma. The high incidence of familial cases indicates the importance of studying the family history of every patient with abdominal symptoms.