This report describes 2 patients with Peutz-Jeghers syndrome, a father and his son, who were shown on barium enema examination to have unsuspected colon carcinoma. Individuals with PJS appear to have a greater tendency to develop gastrointestinal carcinoma than individuals in the general population. The malignant lesions are located predominantly in the colon, stomach and duodenum. The radiologist plays an important role in evaluating patients with PJS and needs to be alert to the possible presence of gastrointestinal malignancy.