Deletion and translocation involving the bands 11q14 and 11q21 have been detected in five patients with T cell acute lymphoblastic leukemia (ALL). The breakpoint on chromosome 11 was on the same band as that previously described in some acute nonlymphocytic leukemias: monocytic or myelomocytic. The existence of a new nonrandom rearrangement involving bands 11q14-q21 is postulated in ALL. An unusual rearrangement on 11q13 in a patient with T cell ALL is also reported.