A retrospective analysis of 49 cases of undifferentiated non-Hodgkin's lymphoma, registered through the Pediatric Oncology Group's randomized clinical trials between 1976 and 1982, suggests that the histologic distinction between Burkitt's and non-Burkitt's tumor is clinicopathologically irrelevant in children. Patients with undifferentiated lymphoma were stratified morphologically into three subtypes: Burkitt's (B; 18 patients); non-Burkitt's (NB; 21 patients); and small noncleaved, not-otherwise-specified (NOS; 10 patients). Median age at presentation was 10 years for B; 12 years for NB; 6 years for NOS; and 10 years overall. Univariate analysis of clinical and laboratory data at presentation, yielded no significant differences between B, and NB patients. Complete remissions were obtained in 75% of the patients, and there were no significant differences in complete remission rate among the different morphologic subtypes of undifferentiated lymphoma. There were no significant differences in the estimated disease free survival between B, and NB patients. No morphologic parameters were identified that were predictive of prognosis.