We report herein a 19-year-old Japanese male with XYY syndrome who developed acute myelogenous leukemia. During three courses of cytotoxic chemotherapy, he suffered repeated hepatic and renal insufficiencies, possibly related to latent dysfunction from the XYY syndrome. The patient was treated with granulocyte colony-stimulating factor combined with etoposide, cytarabine, and busulfan (the latter adjusted to a targeting dose) followed by autologous peripheral blood stem cell transplantation. He had no severe regimen-related toxicities and is now free of leukemia. Am. J. Hematol. 78:55–58, 2005. © 2004 Wiley-Liss, Inc.