OBJECTIVE: Extrapulmonary involvement by Pneumocystis carinii (PC) in acquired immunodeficiency syndrome (AIDS) patients is uncommon. Our purpose is to describe three AIDS patients with low cluster differentiation cell (CD4) counts, who were receiving aerosol pentamidine prophylaxis, and who had large noncalcified hilar and mediastinal lymphadenopathy. MATERIALS AND METHODS: Chest radiography, CT, and clinical and laboratory records of three AIDS patients who had radiographic evidence of mediastinal and hilar lymphadenopathy were retrospectively reviewed. RESULTS: Symptoms were quite similar in all patients: weight loss, fever, cough, and mild dyspnea. Mediastinal and hilar widening was noticed on chest radiography. Contrast-enhanced chest CT revealed multiple noncalcified lymphadenopathy with supracarinal predominance in all cases. Mediastinoscopy with mediastinal and hilar lymph nodes sampling was performed in all patients. Histologic examination of the biopsy specimens demonstrated a necrotic foamy tissue without any calcification, and silver stain coloration showed abundant PC organisms in each case. CONCLUSION: In AIDS patients, PC infection should be considered as a possible cause of noncalcified hilar and mediastinal lymphadenopathy along with such possibilities as atypical infections and neoplasms, especially in severely immunocompromised hosts (low CD4) with aerosol pentamidine prophylaxis.