Although Pneumocystis carinii pneumonia (PCP) usually presents with bilateral interstitial pulmonary infiltrates, many other roentgenographic presentations occur in human immunodeficiency virus-infected patients. To clarify the determinants of atypical presentations of PCP, we evaluated 65 English-language reports that related the roentgenographic manifestations of consecutive cases of PCP. The incidence of PCP-associated upper lobe disease, cysts, and spontaneous pneumothoraxes was increased in human immunodeficiency virus-infected patients receiving aerosolized pentamidine prophylaxis. Normal chest roentgenograms were more common and nodular lesions were less common in human immunodeficiency virus-infected patients than in uninfected patients. However, the roentgenographic manifestations of PCP could not be specifically predicted by a patient's underlying disease. Neither zidovudine therapy nor intravenous drug use apparently affected the roentgenographic presentation of PCP. Unusual pathologic responses to PCP, including granuloma formation, vascular invasion, and microscopic foci of calcification, were present in all patient groups.