PCP remains the leading cause of deaths in patients with AIDS. As familiarity with PCP increases, atypical manifestations of the diseases are being recognized with greater frequency. There are following "atypical" manifestations of PCP ; 1) interstitial lung response that include diffuse alveolar damage, bronchiolitis obliterance, interstitial fibrosis, and lymphoplasmocytic infiltrate 2) striking localized process frequently exhibiting granulomatous features 3) extensive necrosis & cavitation 4) extrapulmonary dissemination of the disease. A wide variety of pathologic manifestations may occur in PCP in human immunodeficiency virus-infected patienst and that atypical features should be sought in lung biopsies from patients at risk for PCP. We had experienced a case of PCP, which presented with severe hypoxia, progressive dyspnea and fine crackles. It was diagnosed as PCP in AIDS with manifestation of BOOP by open lung biopsy and showed good response to Bactrim & corticosteroid therapy.