PURPOSE: To analyze the radiographic and HRCT findings of Pneumocystic carinii pneumonia. MATERIALS AND METHODS: We reviewed the medical records and retrospectively analysed the chest radiographs(n=31) and HRCT scans(n=17) of 31 patients with Pneumocystis carinii pneumonia who had been followed up at our institute between, 1993 and March 1998. Pneumocystis carinii pneumonia was confirmed by cytologic evaluation of sputum stained with methenamine silver(n=25) or on the basis of clinical history(n=6). The study group included 17 men and 14 women aged 28 -78(average, 53.6) years. Twenty-eight patients had underlying conditions such as hematologic diseases(n=13), AIDS(n=8), malignancy(n=2), DM(n=2) and malnutrition(n=1), and three were free from underlying diseases. RESULTS: Twenty patients had pure Pneumocystis carinii pneumonia and 11 had combined lung diseases, namely pulmonary tuberculosis(n=4), pulmonary metastasis(n=2), bacterial pneumonia(n=2), atypical mycobacterial infection(n=1), pulmonary edema(n=1), and Kaposi's sarcoma(n=1). Chest radiographic findings of 20 cases of pure Pneumocystis carinii pneumonia included consolidation(n=12), l inear-reticular opacity(n=8), ill defined haziness(n=7), and nodules(n=6), with bilaterality in is cases and zonal predominance in ten [central(n=5), lower(n=5)]. Ancillary findings included pleural effusion(n=10), cysts(n=5), lymphadenopathy(n=4) and pneumothorax(n=1). In two patients, findings were entirely normal. HRCT findings in ten cases of pure Pneumocystis carinii pneumonia included ground-glass opacity(n=6), consolidation(n=6), linear-reticular opacity(n=8), and nodules(n=5), with bilaterallity in seven cases and zonal predominance in five [central(n=5), lower(n=2)]. Ancillary findings among these cases included pleural effusion(n=4), lym-phadenopathy(n=2), cysts(n=1), and pneumothorax(n=1). HRCT findings in seven cases of Pneumocystis carinii pneumonia combined with other lung diseases included nodules(n=6), ground-glass opacity(n=5), linear-reticular opacity(n=4), and consolidation(n=3). CONCLUSION: Although ground-glass opacity in both pure Pneumocystis carinii pneumonia and this same condition combined with other lung diseases is a common radiologic finding, the possibility of variable radiologic findings in cases of Pneumocystis carinii pneumonia and other lung diseases with which it frequently combines is essential for approximate diagnosis of Pneumocystis carinii pneumonia.