Seventy-seven patients with acquired immune deficiency syndrome (AIDS) and suspected of having Pneumocystis carinii pneumonia (PCP) had flexible bronchoscopy. The diagnosis was established in 52 of the 54 patients (96%) who proved to have PCP. There was one false-positive result. The remaining 22 patients and the patient with the false-positive diagnosis had diseases other than PCP, or no diagnosis. Flexible bronchoscopy is a safe and sensitive diagnostic procedure in patients with PCP complicating AIDS, and is recommended as the first invasive diagnostic procedure when patients at risk for AIDS have acute pulmonary complications.