We observed a polycystic and cavitating presentation of Pneumocystis carinii pneumonia as primary manifestation of AIDS in a patient with previously unknown HIV-infection. Pneumocystis carinii was histologically proved by transbronchial biopsy but not by bronchoalveolar lavage. A nearly complete resolution of all pulmonary lesions could be achieved with cotrimoxazole. Pneumocystis carinii must be considered in differential diagnosis of cystic and cavitating pulmonary disease in patients with unknown or positive serology for HIV-infection.