Even though the close association between AIDS and non-Hodgkin's lymphoma (NHL) is widely known, few studies have evaluated the frequency of gastrointestinal involvement in a large series of AIDS patients with heterogeneous risk factors. We therefore reviewed the demographic and clinical features of patients with AIDS and NHL seen at our institution over a period of 5 years. NHLs complicated AIDS in 70 of 786 (9%) cases in our study. All but one of the tumours were of high- or intermediate-grade histologic subtype, and 80% of 56 patients with diagnosis made during lifetime had disease stages III or IV, most with extranodal localization. The gastrointestinal tract was involved in 23 cases (33%), 13 of whom had an antemortem diagnosis. All these patients complained of significant symptoms, the most frequent being GI bleeding followed by recurrent abdominal pain with or without masses. Three patients had evidence of lymphomatous disease along both the upper and lower GI tract, but more often a single localization was present. Prognosis of patients with NHLs was very poor, and there was no significant difference in survival between patients with and without GI localization at the time of initial diagnosis.