Four years of clinical experience with a fiberoptic intracranial pressure monitor are presented. One hundred forty patients were monitored, of whom 80 had increased intracranial pressure. Of the patients with nontraumatic intracerebral hematoma and subarachnoid hemorrhage, 100% had increased pressure. Forty-seven of 69 patients with head injuries had elevated pressure; of these, 28 had pressure significant enough to require therapy. Both the patients with head injuries and those with nontraumatic hemorrhage were more effectively treated by using the results of pressure monitoring to determine when therapy was required and to indicate the response of the patient to that therapy. Despite the evidence, monitoring of intracranial pressure is not routine due to a lack of acceptance and effectiveness. To overcome such problems, a system must meet the criteria of ease of insertion, reliability, and lack of complications. These criteria are fulfilled by the fiberoptic system presented.