Pneumothorax caused by the rupture of a mycetoma into the pleural space is rarely reported in patients undergoing intensive cytotoxic therapy for hematologic malignancies. We reviewed 46 episodes of mycetoma that developed in 43 patients undergoing antineoplastic therapy; six (13%) of these episodes were further complicated by the occurrence of pneumothorax that developed after bone marrow recovery with return to normal granulocyte count. Etiologic agents included Aspergillus fumigatus, Aspergillus fumigatus plus Blastoschizomyces capitatus, and Mucor (one case each). No pathogen was detected in the remaining three cases of pneumothorax. Four of the six patients died (7, 10, 27, and 50 days after the onset of pneumothorax). Two of the six patients with pneumothorax died of massive hemoptysis, whereas only one of the 40 patients who did not develop pneumothorax died of hemoptysis. This suggests that both pneumothorax and hemoptysis may represent the clinical expression of a more destructive course of invasive fungal diseases.