The objectives of this study were to determine prognostic factors for response to treatment, freedom-from-relapse (FFR) survival, and overall survival of 737 aggressive malignant lymphoma patients treated with the doxorubicin, cyclophosphamide, vindesine, bleomycin, methylprednisolone, methotrexate with leucovorin, ifosfamide, etoposide, asparaginase, and cytarabine (LNH-84) regimen; to construct a prognostic index with factors isolated by multivariate analyses; and to validate this prognostic index with another set of patients. Complete response (CR) was reached in 75% of LNH-84 patients, and 30% of them relapsed. With a median follow-up of 36 months, median FFR survival and median overall survival were not reached. Low serum albumin level, high tumoral mass, weight loss, bone marrow involvement, greater than or equal to 2 extranodal sites, and increased lactic dehydrogenase (LDH) level were associated with a low response rate. Advanced stage, increased LDH level, and nonlarge-cell histologic subtypes (diffuse mixed, lymphoblastic, and small non-cleaved) were statistically associated with a high relapse rate and short FFR survival. Increased LDH level, low serum albumin level, tumoral mass larger than 10 cm, greater than or equal to 2 extranodal sites, advanced stage, and age older than 65 years were statistically associated with short overall survival. Four of these parameters, namely, LDH level, stage, number of extranodal sites, and tumoral mass, were put together to construct a prognostic index. This index partitioned LNH-84 patients into three subgroups of good, intermediate, and poor prognosis (P less than .00001): CR rates of 93%, 83%, and 61%; relapse rates of 12%, 25%, and 45%; 3-year FFR survival of 87%, 73%, and 53%, and 3-year survival of 88%, 71%, and 41%, respectively. This prognostic index was applied to a test set of patients: 155 patients treated on protocols of the Nebraska Lymphoma Study Group. Using this index, these patients had 3-year FFR survival of 70%, 40%, and 22% (P = .0002) and 3-year survival of 79%, 52%, and 31% (P = .005). In patients with aggressive lymphomas, this simple prognostic index could distinguish between patients requiring intensive treatment such as autologous bone marrow transplantation in first complete remission and those who could be treated with standard regimens.