A 65-yr-old man developed increasing dyspnea and fulminant respiratory failure 48 h after introduction of hydroxyurea, oral cytarabine ocfosfate (YNK01) and interferon-α for treatment of Philadelphia chromosome-positive chronic myelogenous leukemia. The chest radiograph showed bilateral patchy infiltrates while computed tomography revealed multiple bullas, ground glass opacities, and patchy consolidations with possible cavitation. Bronchoscopic examination was normal and microbiological tests performed on all biologic fluids were negative. The patient did not respond to multiple antibiotic treatment and corticosteroid administration and died of progressive respiratory failure 5 d after chemotherapy introduction. The postmortem lung examination was consistent with the diagnosis of bronchiolitis obliterans organizing pneumonia (BOOP).