OUTLINE: This is a randomized study. For the first randomization, patients are stratified according to the number of risk factors (0-1 vs 2-4). For the second randomization, in addition to the number of risk factors, patients are stratified according to objective response to initial induction therapy (partial response vs complete response) and induction therapy (CHOP vs CHOP and rituximab). Patients are randomized to one of two treatment arms. Arm I: Patients receive CHOP chemotherapy comprising cyclophosphamide IV, doxorubicin IV, and vincristine IV on day 1 and oral prednisone on days 1-5. Treatment repeats every 21 days in the absence of unacceptable toxicity. Arm II: Patients receive treatment as in arm I. Patients also receive rituximab IV on days -7,-3, 41, and 83. Patients who achieve complete response (CR) after 4 courses of CHOP and remain in CR after 6 courses of CHOP are further randomized to one of two arms. Arm I (Maintenance therapy): Patients receive rituximab IV weekly for 4 weeks. Courses repeat every 6 months for 2 years in the absence of unacceptable toxicity. Arm II: Patients are observed. Patients who achieve partial response (PR) after 6 courses OR PR after 4 courses and then CR after 6 courses receive 2 additional courses of CHOP therapy. Patients are then also randomized to receive either maintenance therapy or observation as above. Patients with stable disease or disease progression are removed from the study. Patients are followed every 3 months for 2 years, every 6 months for 3 years, and then annually thereafter.