The frequency and characteristics of childhood acute leukemia with a 14q32 translocation [other than the t(8;14)(q24;q32)] were determined in 335 cases of newly diagnosed acute lymphoblastic leukemia (ALL) and 105 cases of acute nonlymphoblastic leukemia (ANLL). Ten children, representing 2.3% of the entire cohort, had this abnormality (1.5% of ALL patients and 4.8% of ANLL patients). By French-American-British (FAB) criteria, 4 cases were classified as L1, 1 as L2, 2 as M1, 1 as M2, and 2 as M5. Remarkably, mixed-lineage expression was found in 6 of these 10 cases, but in only 21 of the other 430 cases without a 14q32 translocation (P less than .001). Leukemic cells from 5 of these 6 cases (4 ANLL, and 1 ALL) coexpressed CD13, a myeloid-associated antigen, and CD2, a T-cell-associated antigen; blasts from the sixth case (ALL) coexpressed CD13 and CD19, a B-lineage-associated antigen. Thus, in addition to the well-described 11q23 translocations and t(9;22), 14q32 translocations also appear to be associated with mixed lineage antigen expression. Break-points of the reciprocal chromosomes from chromosome 14 were identified in five of these cases: 1q23, 6q23- q25, 7p15, 8q11, and 12q13. Of the four mixed-lineage cases that were tested, none showed rearrangement of the immunoglobulin heavy chain (IgH) gene. This suggests that the 14q32 breakpoint does not involve the IgH gene and that an unidentified important gene may reside on 14q32.