Spontaneous pneumothorax in AIDS patients with recurrent Pneumocystis carinii pneumonia despite aerosolized pentamidine prophylaxis. Aerosolized pentamidine prophylaxis for Pneumocystis carinii pneumonia in patients with the acquired immunodeficiency syndrome (AIDS) may predispose these patients to recurrent apical Pneumocystis infection. Bullous changes and pulmonary cysts develop in the lung apices due to repeated episodes of inflammation and cytotoxic effects of HIV on pulmonary macrophages. These changes progress despite prophylaxis against recurrent Pneumocystis infection with aerosolized pentamidine, increasing the risk of spontaneous pneumothorax. Two cases are presented of bilateral pneumothoraces in patients with AIDS and recurrent P carinii pneumonia despite aerosolized pentamidine prophylaxis. Patients receiving aerosolized pentamidine prophylaxis for Pneumocystis pneumonia appear to have an increased risk of pneumothorax due to recurrent apical infections with P carinii. 