Eight cases of intracranial arachnoid cysts are reported. They are benign congenital lesions who result from an abnormal development of the earliest arachnoid. A subsequent development is possible. The macrocephaly is the first sign and other symptoms give evidence to the localization. Thanks to the C.T. scan one can make the diagnosis, appraise the repercussion and put the therapeutic indications. The surgical treatment is reserved to symptomatic forms. The peritoneal shunt takes the ablation's place. This method is easier and less liable to complications. The results depend on the localization, the pattern of operation and the precocity of the diagnosis.