Pericardial effusion is a rare but potentially life-threatening complication of chronic myelomonocytic leukemia. A case of a 70-year-old female with CMML is reported, who developed a severe pericardial effusion after an initially stable course of disease. She underwent pericardiocentesis and subsequent intracardial instillation of mitoxantrone with poor response. Subxiphoid pericardiotomy was successfully performed. Leukocytosis did not respond to hydroxyurea. Because of decreasing performance status of the patient systemic chemotherapy was not applied and the patient died within 2 weeks. A review of the literature shows that there is no effective treatment for pericardial effusion in CMML, and some common features may be noted.