Pleural effusion in 4 patients with chronic myelomonocytic leukemia (CMML) is described in this report. According to the literature, pleural effusion in CMML is a poorly understood and rare occurrence. Two of our patients presented with pleural effusion as an initial symptom while the other 2 developed it during the course of the disease. In only 1 patient was the pleural effusion due to leukemic infiltration while in the other 3 it was a reactive phenomenon. Peripheral lymphadenopathy was observed only in the former patient who died of acute leukemia. After prednisolone therapy the pleural effusions resolved in the other 3 patients.