Pneumocystis carinii pneumonia (PCP) presenting as bilateral upper-lobe cavitary disease is rare. Isolated upper-lobe involvement has traditionally been associated with aerosolized pentamidine prophylaxis. Dapsone is a cheap and effective prophylactic agent against P carinii in patients who cannot tolerate trimethoprim-sulfamethoxazole. This is a case of a man who presented with bilateral upper-lobe cavitary P carinii pneumonia despite being on dapsone prophylaxis. Bronchoalveolar lavage was negative for P carinii. Transbronchial biopsy was positive for P carinii. The patient improved significantly with radiological resolution on specific treatment for P carinii. PCP should be included in the differential diagnosis of upper-lobe cavitary lung disease, and a transbronchial biopsy should be performed when the diagnosis is suspected.