Approximately 35% of T-cell acute lymphoblastic leukemia (T-ALL) cases have chromosomal translocations as evaluated by conventional cytogenetic methods (G-banding). Some chromosomal translocations are associated with morphologically and immunophenotypically distinct leukemia subtypes and define patients with different clinical outcomes. Chromosomal translocations may deregulate gene expression, thus contributing to the development of neoplasia, either by placing a putative oncogene under the control of strong regulatory elements or by generating chimeric genes and oncogenic fusion proteins. We report here a novel der(12)t(7;12)(p15;q24.3) in a child with T-ALL. Cloning and characterization of the breakpoint region may contribute to the discovery of new genes that are important in T-ALL.