Twelve patients (10 males, 2 females) with symptomatic arachnoid cysts of the middle cranial fossa (9 patients) or overlying the frontal cortex (3 patients) were included. Under local anesthesia, an internal shunt was implanted from the cyst to the subdural compartment. Postoperative computed tomography scans showed volume reduction in eight patients. Permanent clinical improvement was also seen in eight patients. In the remaining four, the improvement was only temporary or partial, necessitating additional surgery in three patients. Complications (two subdural hematomas, one subdural infusion), were observed in three patients, all with large cysts. The complications were treated without sequelae. Internal shunts may be tried in adults as the first treatment for this condition.