The records of 150 primary gastrointestinal (GI) lymphomas in adults collected from 1974 to 1982 at the Department of Pathology, University of Vienna, were reviewed. One hundred thirty-three cases of malignant lymphomas (ML) were analyzed with respect to histologic type, presenting tumor stage, and clinical course, as well as for factors influencing prognosis. The histologic type of ML as assessed by the Working Formulation and the Kiel, the Lukes and Collins, and the Rappaport classifications showed only a minor influence on prognosis. MLs of follicular center cell origin prevailed in the stomach and large cell, immunoblastic MLs prevailed in the bowel. Immunoperoxidase studies indicated a B-cell nature of GI MLs and demonstrated intracytoplasmic IgM kappa or lambda in most of the MLs of the small lymphocytic, plasmacytoid, and immunoblastic type, respectively. The 105 cases of gastric MLs represented 3.6% of all malignancies of the stomach collected during the study period. Clinical symptoms preceded the diagnosis by 4.4 months on average, and endoscopic biopsy specimens indicated malignancy in 78%. Presenting tumor stages of gastric MLs according to the Ann Arbor staging system were Stage I in 20%, Stage II in 76.2%, and Stage IV in 3.8%. The 28 cases of intestinal ML localized in the small and large bowel without any site prevalence presented with Stage I in 14%, Stage II in 82%, and Stage III in 4%. Tumor resection was performed in 90% of all cases and was followed by multiagent therapy in 53%. Radical tumor resection was obtained in 58% of the gastric MLs and only 28.6% of the intestinal MLs and was closely related to tumor stage. Statistical analysis demonstrated a significant influence of the presenting tumor stage on prognosis as expressed by the overall 2-year survival rate of 70% for Stage I versus 39% for Stage II ML. In addition, Stage II1 according to Musshoff et al. run a better course than II2 as shown by the disease-free 2-year survival rate of 49% versus 15%, respectively. Radical tumor resection was a major determinant of survival and cure of disease as exhibited by the disease-free 2-year survival rate of 57% after radical resection versus 8% after nonradical resection of ML. Finally, diffuse tumor growth and tumor penetration of the gastric wall beyond serosa decreased the survival rates.