Objective To study the clinical characteristics, diagnostic methods and therapeutic efficacy of pneumocystis pneumonia (PCP) in patients with acquired immunodeficiency syndrome (AIDS). Methods Sixty-nine AIDS cases of PCP were diagnosed according to the criteria of USA Centers for Disease Control and Prevention revised in 1993. The clinical symptoms and signs of the patients were observed. The peripheral blood lymphocyte counts, blood gas analysis and bronchoalveolar lavage fluid (BALF) were checked and transbronchoscopic lung biopsy was performed. Results All studied patients were in the late stage of AIDS. The main clinical manifestations included fever (100.0%), cough (97.1%), and dyspnea (92.80%). Pulmonary rales could be heard in 42 cases (60.9% ). Peripheral CD4+ T lymphocyte counts ranged from 1 × 106 -88 × 106/L. Fifty-two cases (75.4% ) had low arterial partial pressure of oxygen value of less than 10.7 kPa (1 kPa = 7.5 mm Hg). Sixty-one cases (88.4 %) had elevated serum lactate dehydrogenase (LDH) level. Bilateral diffused interstitial change (46.4%) and ground-glass shadow (29.0%) were the most common abnormal chest radiological findings. Pneumocystis organisms were detected in the BALF from 2 patients and in the transbronchial biopsy (TBB) tissue from 35 patients. All patients were treated with compound sulfamethoxazole. Thirty-three were treated with corticosteroid simultaneously and 27 were assisted with mechanical ventilation. Fifty patients recovered or got improved, eleven died, and eight left hospital because of deteriorated condition. Conclusions When an AIDS patient represents with fever, cough, dyspnea, hypoxemia, elevated serum I.DH level, CD4+ T lymphocyte count below 100 × 106/L, and interstitial pneumonia or ground-glass shadow in chest images, the diagnosis of PCP could be made presumptively. It is difficult to make a nosogenic diagnosis of PCP, but TBB considerably increases the positive rate of pneumocystis. Compound sulfamethoxazole is recommended as the first selected drug. In severe cases, corticosteroid and assisted mechanical ventilation combined with compound sulfamethoxazole could remarkably improve the prognosis of PCP.