A 28-year-old man was admitted to our hospital because of cardiac tamponade and pleural effusion. Although his peripheral blood picture was normal, his pericardial fluid contained a lot of myeloblasts with Auer bodies and a diagnosis of acute myeloblastic leukemia (M2) was made from the finding of bone marrow smears. The pericarditis was successfully treated with instillation of mitoxantrone into the pericardial space after drainage. He responded well to the systemic chemotherapy and achieved a complete remission. Although 27 cases of leukemia complicated with cardiac tamponade have so far reported, only three cases gave normal findings of the peripheral blood on admission. Leukemic pericardial effusion with cardiac tamponade in very rare as an initial manifestation of AML. The efficacy and safety of pericardial infusion of mitoxantrone were demonstrated in this patient.