We report the first Japanese case of acute promyelocytic leukemia with t(11;17)(q23;q21) and CD56. A 41-year-old man with schizophrenia was hospitalized because of the appearance of blasts with Auer bodies in his peripheral blood. A bone marrow smear showed an abundance of abnormal cells with scanty azurophile granules in the cytoplasm and somewhat lobulated nuclei. Because the abnormal cells demonstrated strongly positive peroxidase reactivity with a few faggot bodies, the patient was given a diagnosis of acute promyelocytic leukemia (M3v according to the FAB classification). However, chromosome analysis revealed t(11;17)(23; q21). All-trans retinoic acid (ATRA) was not effective. Mitoxantrone was more effective than daunorubicin, and resulted in a complete remission with a normal karyotype. About 9 months later, the patient suffered a relapse. Surface marker analysis demonstrated blasts that were positive for CD56, CD13, and CD33. MEC (mitoxantrone, etoposide, cytarabine) therapy was ineffective. Although ATRA was administered at a dose of 80 mg/day for more than 2 months, the number of myelocytes and promyelocytes increased Finally CAG (cytarabine, aclarubicin, G-CSF) therapy was initiated, but the patient died due to intracranial invasion and hemorrhage accompanied by disseminated intravascular coagulation.