We retrospectively analysed CT findings of 47 cystic brain lesions of 44 patients, in which operation, biopsyof follow-up study was needed for their final diagnosis. The resullts were as follows: 1. The etiologic disease of cystic brain lesions were 15 cases of brian abscess, 9 cases of astrocytoma, 5 cases of glioblastoma multiforme, 3cases of metastasis. 2. We analyses the cystic lesions in view of their number, location, shape, perifocal edema,mass effect, 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% of metastases were multiple in number,but the remaninder showed single lesion. b. The shape of cystic lesions were round or ovoid in 68%, lobulated in8.5% and irregular in 23.5%, and no demonstrable difference of shape were noticed in different disease. c. Inbrain abscess, the wall of cystic lesions tend to be thin, even and smooth in inner surface, but the outersurfaces were equally smooth or irregular. d. Mural nodules were found in nearly half of the cases of astrocytoma,glioblastoma mutiforme, metastasis and hemangioblastoma, but the brain abscess and dermoid cyst contained no muralnodule. e. Meningiomas were found to be attached to dura mater and showed thickening of the inner table ofadjacent skull or of the falx. f. The presence of preceding infectious disease may be helpful in the diagnosis ofbrain abscess, but in 20% there were no demonstrable preceding infection. g. Lung cancer was confirmed as primarysite in two of the cystic metastatic disease, but other 2 cases showed no demonstrable primary malignancy.