To correlate the histologic subtype of diffuse large cell (DLC) lymphoma with immunophenotype, clinical features, and treatment outcome, 88 consecutively diagnosed children with this disease were studied. Of these cases, 42 (48%) were immunoblastic (IB), polymorphous subtype; 17 (19%) IB, plasmacytoid; 8 (9%) IB, clear cell; 6 (7%) IB, not otherwise specified; and 15 (17%) DLC-follicular center cell (DLC-FCC) type. Of 34 cases successfully phenotyped from paraffin sections, 13 were T cell and 9 were B cell; of the remaining cases, 8 were suggestive of T-cell lineage, 3 of B-cell lineage, and 1 of histiocytic differentiation. Although histologic subtype did not correlate with clinical features or outcome, it did correlate with immunophenotype among those cases for which lineage could be unequivocally assigned (5 of 18 IB vs. 4 of 4 DLC cases were B cell; P = 0.02) Immunophenotype was also correlated with stage of disease (11 of 13 T-cell vs. 3 of 9 B-cell cases had stage III-IV disease; P = 0.03). (Stage III includes all primary thoracic tumors; stage IV includes all with central nervous system and/or bone marrow involvement.) Significant prognostic features were clinical stage and era (thus type) of therapy (P less than 0.001). The authors conclude that most cases of large cell non-Hodgkin's lymphoma in children are of IB morphologic type, most frequently of T-cell lineage, and those with T-cell phenotype appeared to have more advanced disease.