Arachnoid cysts are benign developmental cysts that occur in the cerebrospinal axis in relation to the arachnoid membrane, and contain clear, colorless fluid resembling normal cerebrospinal fluid. Authors retrospectively analysed 24 brain CT scans of 23 patients with pathologically proven arachnoid cysts that were examined at Wonju Christian Hospital from jan. 1985 to Dec. 1989. The results were as follows; 1. The common clinical symptoms were headache(9cases), others were hydrocephalus, visual distrubance and bulging of the scalp. 2. Arachnoid cysts in supratentorial region were 14 cases, most of them were located in middle cranial fossa(9cases), and infratentorial locations were 10 cases, most of them were located in retrocerebellar area(7cases). 3. Shape of the arachnoid cysts were quadrangular with straight inner margin(11 cases), spherical with convex inner margin(8cases), and others(5cases). 4. Of 14 cases with supratentorial region, most of them(10 cases) showed quadra gular shape with straight inner margin. Of 10 cases with infratentorial region, most of them(7cases) showed spherical shape with convex inner margin. Of 9 cases with middle cranial fossa region, most of them(8cases) showed quadrangular shape with straight inner margin. 5. Size of the arachnoid cysts, in the greater diameter was commonly distributed between 3 and 7 cm(12 cases)