We retrospectively analysed CT findings of 47 cystic brain lesions of 44 patients, in which operation, biopsy or follow-up study was needed for their final diagnosis. RESULTS : 1. The etologic diseases of cystic brain lesions were 15 cases of brain abscess, 9 cases of astrocytoma, 5 cases of glioblastoma multiforme, 3 cases of meningioma, 5 cases of craniopharyngioma, 1 case of hemangioblastoma, 2 cases of dermoid cyst and 4 cases of metastasis. 2. We aalyses the cystic lesions in view of thir number, location, shape, perifocal edema, mass efect, wall and its thickness, evenness and characteristics of their inner and outer surfaces, mural nodule, calcification and contrast enhancement. a. 13.3% of brain abscess and 75% fo metastases were muliple in number, but the remainder showed single lesion. b. The shape of cystic lesions were round or ovoid in 68%, lobulated in 8.5% and irregular in 23.5%, and no demonstrable difference of shape were noticed in different disease. c. In br in abcess, the wall of cystic lesions tend to be thin, even and smooth in inner surface, but the outer surfaces were equally smooth or irregular. d. Mural nodules were found in nearly half of the cases of astrocytoma, glioblastoma multiforme, metastasis and hemangioblastoma, but the brain abscess and dermoid cyst contained no mural nodule. e. Meningiomas werefound to be attached to dura mater and showed thickening of the inner table of adjacent skull or of the falx. f. The presence of preceding infectious disease may be helpful in the diagnosis of brain abscess, but in 20% there were no deonstrable preceding infection. g. Lung cancer was confirmed as primary site in two of the cystic metastatic disease, but other 2 cases showed no demonstrable primary malignancy.