Patients with acquired immune deficiency syndrome (AIDS) may be infected with many opportunistic pathogens, the most common of which is Pneumocystis carinii. P. carinii infection typically presents as a subacute pneumonia. However, rare cases of localized, extrapulmonary, and disseminated disease have been described. Standard therapy for P. carinii is systemically administered trimethoprim-sulfamethoxazole or pentamidine. These agents, however, frequently are associated with serious adverse effects. More recently, aerosolized pentamidine has been proposed as an alternative treatment for those who cannot tolerate standard therapy and as primary and secondary prophylaxis. Inhaled pentamidine is effective, but it is not without hazards. The authors describe a patient with AIDS who received long-term treatment with aerosolized pentamidine and yet died as a result of widely disseminated P. carinii infection.