From May 1979 to March 1983, 93 eligible patients with nonlymphoblastic lymphoma (NLBL) were treated by members of the Pediatric Oncology Group (POG) with Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), vincristine, prednisone, cyclophosphamide, and mercaptopurine (ACOP+); CNS prophylaxis with intrathecal (IT) methotrexate, hydrocortisone, and cranial irradiation (2,400 rads), and radiation therapy to the primary disease were administered in stages I and II, and to residual disease in stages III and IV. Duration of treatment was 2 years for stages I, II, and III and 3 years for stage IV disease. Of the 93 patients entered onto the study, 47 had diffuse small noncleaved-cell lymphoma (DSNCL), 38 had diffuse large-cell lymphoma (DLCL), and eight had other histologies. Localized disease (stages I and II) was present in 51 patients, and 42 had advanced (stages III and IV) disease. The study confirmed previously reported importance of stage with a 4-year event-free survival (EFS) of 78% (SE +/- 7%) for patients with localized disease as compared with 44% (SE +/- 9%) in patients with advanced disease (P less than or equal to .001). In localized disease, seven of 11 adverse events occurred in patients who were off therapy and more than 30 months after the initial diagnosis (relapse, three; second malignancy, two; death in remission, two). Large-cell histology proved to be an important prognostic factor in patients with stages III and IV disease with EFS at 4 years of 67% (SE +/- 11%) for DLCL versus 17% (SE +/- 11%) for DSNCL (P less than or equal to .001). We conclude that it is important to distinguish histologically between small noncleaved-cell and large-cell types of NLBL as a basis for further controlled clinical trials.