Philadelphia (Ph) chromosome-positive acute myelogenous leukemia (AML) is a rare disease that is resistant to conventional antitumor chemotherapy and has a poor prognosis. We describe a case of Ph chromosome-positive AML in which imatinib mesylate was used and a favorable outcome was obtained.A 64-year-old man was found to have Ph chromosome-positive, minor BCR-ABL-positive AML. Remission could not be induced by remission induction therapy with antitumor agents. Because the patient had a serious concomitant infectious disease, administration of 600 mg/day of imatinib mesylate, a specific inhibitor of BCR-ABL tyrosine kinase, was started after written informed consent was obtained. Complete cytogenetic response (CCR) was achieved without serious adverse events and persisted for more than 1 year. Our results suggested that imatinib mesylate was very useful for treating Ph chromosome-positive AML.