After an analysis of the patients treated in the last five years, a report is given on 9 cases of arachnoid cysts as a rare form of intracranial space occupation. The etiology of the arachnoid cysts has not been fully cleared up yet, but the semipermeability of the cyst membrane appears to be an important pathogenetic factor. Today, the diagnosis of the disease is verified by CT techniques. In case of the occurrence of clinical symptoms the treatment should always be carried out in the form of an operation.