Twenty-two cases of intracranial arachnoid cysts in adult patients have been studied and treated surgically. The authors analysed the correlation between the size and the location of the cysts and their clinical manifestations. It seems clear that the symptomatology and the problems of intracranial arachnoid cysts in the adult are quite different from those occurring with infants. The majority of our cases have been diagnosed by CT and NMR, and have been treated by open excision of the cystic membranes with the establishment of a wide communication with the basal cisterns or the subarachnoid space. With this technique the results have been very gratifying, while in cases managed with shunts the morbidity has been high.