In the 1980s, under the impact of the acquired immune deficiency syndrome, Pneumocystis carinii Pneumonia (PCP) has become the prime infectious manifestation of this condition. In addition to the well-recognized "classic" features of this disease, several unusual manifestations are being recognized with increasing frequency. We presently review and illustrate the following "atypical" manifestations of PCP: (1) interstitial lung responses that include diffuse alveolar damage, bronchiolitis obliterans, interstitial fibrosis, and lymphoplasmacytic infiltrates; (2) striking localized processes frequently exhibiting granulomatous features; (3) extensive necrosis and cavitation; and (4) extrapulmonary dissemination of the disease. Close clinico-pathologic correlation and attention to roentgenographic detail are invaluable aids in arriving at the correct diagnosis.