One case of acquired immunodeficiency syndrome (AIDS) complicated with Pneumocystis carinii pneumonia was retrospectively reviewed. The clinical manifestations and histopathological changes were analyzed. After a positive diagnosis of AIDS by laboratory examinations, the patient underwent a bronchoscopic lung biopsy. Pneumocystis carinii was detected in the obtained lung tissues by Gomori’s methenamine silver staining (GMS) and periodic acid­Schiff staining (PAS). With a sulfamethoxazole (SMZ) treatment, the patient recovered from pneumonia. AIDS patients are vulnerable to Pneumocystis carinii, and the complication often leads to interstitial pneumonia. The physicians should take measures to consider possible Pneumocystis carini infection and to select effective treatment after a positive detection.