All human immunodeficiency virus type 1 (HIV-1) infected adult patients referred to the Division of Pulmonary Diseases of the Centre Hospitalier de Kigali, Rwanda for evaluation of a pulmonary disease of undetermined etiology (PDUE) were investigated by fiberoptic bronchoscopy using both bronchoalveolar lavage (BAL) and transbronchial biopsy (TBB). During a 10-mo period 111 HIV-1 infected patients with PDUE were examined, of whom 47 (42%) fulfilled the World Health Organization (WHO) clinical case definition for acquired immunodeficiency syndrome (AIDS) and seven (6%) had an AIDS-defining illness. Nonspecific interstitial pneumonitis was diagnosed in 42 (38%) patients, tuberculosis in 25 (23%), cryptococcosis in 14 (13%), Kaposi's sarcoma (KS) in 10 (9%), Pneumocystis carinii pneumonia (PCP) in five (5%). The diagnosis remained undetermined in 18 (16%) patients. Chest radiograph patterns were generally nonspecific. TBB and BAL had diagnostic yields of 82 and 26% of all final diagnoses, respectively. Our study on Rwandese HIV-1-infected patients with PDUE provides evidence for a large spectrum of pulmonary diseases with relative frequencies differing strikingly from those in developed countries. Detailed investigations confirm the rarity of PCP in Africa and highlight nonspecific interstitial pneumonitis as the predominant diagnosis of PDUE. Empiric antituberculosis treatment is justified in the absence of clinical manifestations suggestive of a specific diagnosis and while awaiting the results of the diagnostic procedures. Primary prophylaxis for PCP would not be appropriate in Africa.