Fifty-five patients with celiac disease and coexistent malignant disease (27 lymphoma, 28 other malignancies) are described. The important clinical features at presentation of lymphoma were weight loss, abdominal pain, diarrhea, profound weakness and fever, associated with anemia, raised ESR, hypoalbuminemia and steatorrhea. There were no specific features to enable earlier diagnosis. Radiology was unhelpful and in no case were malignant cells seen in the jejunal biopsy. Four of the lymphomas were Hodgkin's disease, none of which involved the bowel; the remainder were reticulum cell sarcoma, 17 of which involved the bowel. Definitive diagnosis prior to death was made in only 18 patients, of whom 16 survived from 2 to 226 days (mean, 76 days). Of the remaining two patients, one is still alive, while the other died 26 years after the original diagnosis of Hodgkin's disease. The possibility of lymphoma should be considered in those who present with celiac disease in middle life and in those who deteriorate for no apparent reason after a period of stability on a gluten-free diet. The index of suspicion for lymphoma in celiac disease should be high and early laparotomy be considered in patients with unexplained deterioration. Twenty-eight patients with 29 carcinomas and 3 other tumors are also described. The presentations of these malignancies were no different from their presentations in non-celiac patients, and their development did not provoke a relapse of celiac disease. Considering the whole series of 55 patients, there was little evidence for the view that malignancy itself was the cause of the flat jejunal mucosal appearances seen in these patients.