A retrospective clinicopathological study was performed on 149 patients who developed malignant lymphoma at under 20 years of age and were diagnosed and treated at the National Cancer Center Hospital between 1962-1986. Using the Japanese Lymphoma Study Group classification (and Working Formulation), we reclassified the 84 evaluable tissue specimens as follows: follicular large and mixed lymphoma (two cases), diffuse lymphoblastic lymphoma (40 cases), Burkitt's lymphoma (small noncleaved, SNC) (12 cases), diffuse large and mixed cell lymphoma (25 cases), and unclassified (five cases). The age of the patients ranged from 6 months to 20 years, with a median of 11 years. The clinical characteristics were found to depend upon the histological diagnosis, as reported previously. To evaluate the influence of various clinical and morphological parameters on survival, univariate analysis was performed for each histological subtype. In lymphoblastic lymphoma, patients with a mediastinal mass had significantly earlier development of leukemic conversion and a shorter survival than patients without a mass. Because of the small number of patients and their short survival, no significant prognostic factors were found in Burkitt's lymphoma (SNC). In large and mixed cell lymphoma, response to therapy was the most significant prognostic factor. As therapy became more intense and systematic throughout the study period, the complete remission rate and survival improved steadily. Autopsy findings confirmed that lymphoblastic lymphoma and Burkitt's lymphoma (SNC) spread systemically earlier than large and mixed cell lymphoma.