Twenty-eight cases of intracranial arachnoidal cysts diagnosed during the period 1978-1990 are analyzed. All cases were investigated with computed tomography (CT), 5 with magnetic resonance imaging (MRI) and 5 with ultrasonography (US). Seventeen were located in the middle cranial fossa, 3 in the quadrigeminal cistern, 2 were parasagittal, 3 suprasellar and 3 were located in the posterior fossa. Twenty-three of the 28 patients were treated surgically, craniotomy with fenestrations was used in 3 cases. Different varieties of shunts were inserted in 8 cases and in the last 15 patients the only surgical treatment was the insertion of cysto-peritoneal (CP) drainage (without a valve) with excellent results. MRI and/or CT follow-up revealed disappearance of the cyst in 13 out of 22 cases and 7 experienced a marked reduction. In 2 patients the cyst showed little change. There were no cases of infection and no deaths.