A pneumothorax occurred in a 29-year-old HIV-positive woman with rapidly progressive dyspnoea at rest and left-thoracic pain, dry cough and fever. Sputum test revealed Pneumocystis carinii pneumonia. Treatment was started with 20 mg/kg trimethoprim and 100 mg/kg sulfamethoxazole, but was poorly tolerated and changed for pentamidine, 4 mg/kg i.v. from the fifth day onwards. A chest drain was inserted, but pleurodesis became necessary after two further lung collapses. After three weeks secondary prophylaxis of the Pn. carinii pneumonia was started with pentamidine inhalations (60 mg every two weeks). The patient gradually improved under this regimen. Pneumothorax is a rare complication of Pn. carinii pneumonia, but should be considered in patients with rapid respiratory deterioration. In addition, Pn. carinii pneumonia should be considered in HIV-positive patients with pneumothorax.