In 11 cases of intracranial, temporal arachnoid cysts the etiology, clinical and radiographic findings, surgical treatment, and outcome are reviewed in respect of post-traumatic subdural hematoma. Cysts of the middle cranial fossa are susceptible to trauma, which may cause bleeding either into the cyst or into the subdural space. Signs and symptoms of increasing intracranial pressure (ICP), local neurological deficits, and sometimes epileptic seizures may lead to hospitalization. CT or MRI scans are diagnostic in these cases. In cases of intracranial mass lesion with displacement of the midline structures and increasing ICP, osteoplastic craniotomy is performed and the lateral wall of the cyst is resected down to the tentorial notch by a microsurgical procedure, with opening into the basal cisterns. There were no operative or postoperative complications in 11 consecutive cases. However, one boy required a cystoperitoneal shunt 3 months later as a result of hydrocephalus following subdural hematoma. Asymptomatic arachnoid cysts are discussed with respect to brain function and social behavior.