Eight patients with AIDS and Pneumocystis carinii infection were studied. Protean manifestations were a feature not untypical of disseminated pneumocystosis. Aerosolised pentamidine as prophylaxis against P carinii pneumonia was ineffective at suppressing dissemination. The knowledge that extrapulmonary infection can occur has implications for the detection and treatment of, and prophylaxis against, P carinii infection. The survival of patients with disseminated pneumocystosis is particularly poor, and may be due to a lack of clinical awareness and consequent delay in diagnosis.