In chronic myelogenous leukemia (CML), pericardial effusions are rarely seen. Pericardial tamponade may occur in many of the patients with pericardial effusion. Here in a 45-year-old male with newly diagnosed chronic phase of Philadelphia chromosome (the Ph)-positive CML, asymptomatic pericardial effusion was detected by echocardiography. The pericardial effusion disappeared after chemotherapy without pericardiocentesis, within six months. Pericardial effusion should always be suspected in patients with chronic phase of CML, even though they are asymptomatic. In our case the pericardial effusion was probably due to extramedullary haematopoiesis because it improved with chemotherapy. Follow-up with echocardiography was sufficient in this case.