A total of 813 patients admitted to Roswell Park Memorial Institute from 1963--1972 with non Hodgkin's lymphoma (NHL) were reviewed for gastrointestinal (GI) involvement. Primary involvement was found in 71 and secondary involvement in 31 patients. Occult GI involvement was detected in 46% of the autopsy cases. The median survival time after the diagnosis of secondary GI involvement was nine months. The occurrence of primary GI-NHL was: 33 in the stomach, 18 in the small intestine, 14 in the ileocecal area including appendix, and 6 in the large intestine. Retrospective staging according to the Ann Arbor staging classification showed 24 to have presented as Stage I, 30 as Stage II, 4 as Stage III, and 13 as Stage IV. The primary diagnostic and therapeutic approach was operative, except in 2 patients with rectal lymphoma. Resection of the principally involved site was carried out in 42 patients. The remainder had palliative procedures or biopsy examinations only. Postoperative radiation therapy was given to 38 patients. Prognostically important features for primary GI-NHL were: stage; histologic type; site of the primary disease; and whether or not radiotherapy was administered. The age of the patient, size or degree of local extension, and type of operative procedure were prognostically of no importance. The results of this study would indicate that in Stage I and II primary GI-NHL, elective resection is not necessary prior to radiation therapy and that resection alone cannot be considered adequate treatment. A modified staging classification is proposed.