In this paper, we report on a 9-year-old girl with acute nonlymphocytic leukemia (FAB-M5) with a rare chromosome abnormality, t(11;23)(q21;p11). Peripheral blood showed Hb 7.5 g/dl, WBC 3,600 cells/microliters (10% blasts), and platelet count 110 x 10(3) cells/microliters. The bone marrow aspirates showed normal cellularity with 36.7% blasts. On morphological characteristics, micromegakaryocytes were observed, and on chromosome examination the karyotype was shown to be 46,XX,t(11;13)(q21;p11) in all metaphases.