Arachnoid cysts can occur through inflammatory, traumatic, chemical irritation, skin tumor and postoperative processes. It is diagnosed and differentiated by magnetic resonance imaging and computerized tomography from other lesions. Its differential diagnosis includes colloid cyst , craniopharyngioma, prosencephaly, holoprosencephaly , epidermoid cyst, hydatid cyst, low grade glial tumors, infarcts and subdural hygroma. Most of them are asymptomatic and diagnosed incidentally. Treatment methods such as simple cyst aspiration , total excision of the cyst, basal cysternostomy, ventricular fenestration, cysto or ventriculoperitoneal shunt can be performed by various endoscopic surgery and craniotomy.