In the World Health Organization classification, cases with classical Burkitt morphologic features and a very high proliferation fraction but without the MYC translocation are not clearly designated as a separate entity and are usually categorized as diffuse large B-cell lymphoma (DLBCL). We identified from our records 33 cases of highly aggressive mature B-cell neoplasms from 8 children and 25 adults with typical Burkitt cytomorphologic, histologic, and immunophenotypic (CD20+/CD10+ and surface immunoglobulin-positive) features. Rearrangement of MYC (MYC+) was present in only 18 of 33 cases, but the proliferation fraction was more than 90% in all MYC-cases (no MYC rearrangement). The immunophenotype of the lymphoma cells in the 2 groups was similar. Although children with MYC+ and MYC- neoplasms were treated with chemotherapy regimens appropriate for Burkitt lymphoma, adults with MYC- lymphomas received less aggressive therapy usually given for DLBCL. Survival analysis showed that adults in the MYC- group had an inferior outcome compared with adults with MYC+ disease. Provisional identification of MYC- lymphomas with typical Burkitt morphologic features as an entity separate from DLBCL will facilitate further studies and possible categorization as a separate entity.