A retrospective study was conducted to determine the influence of the acquired immunodeficiency syndrome (AIDS) epidemic on the incidence, clinical presentation, and outcome of primary gastrointestinal lymphoma (stages I and II) over a 20-year period at a single institution. Between 1971 and 1981, there were seven cases. Fifty-eight patients were diagnosed between 1983 and 1993, and 81 per cent were AIDS-related. The mean age overall was 50 years; 81 per cent were male, and 35 per cent presented with acute complications. All tumors were high or intermediate grade B cell lymphomas, and 48 per cent had bulky or advanced disease at presentation. The overall actuarial 5-year survival was 9 per cent. Human immunodeficiency virus status and stage were significant independent prognostic factors. The AIDS-related subgroup had a mean age of 43 years, and 91 per cent were male. Tumor resection was performed in 38 per cent, and the 5-year survival was 2 per cent. The mean age for the non-AIDS-related subgroup was 71 years, and 55 per cent were male. Resection was performed in 39 per cent, and 5-year survival was 28 per cent. AIDS-related disease accounted for the dramatic increase in incidence of primary gastrointestinal lymphoma since 1983. The prognosis for these patients is poor and is dominated by the underlying immunocompromise.