In 45 out of 103 cases with chronic subdural hematoma a definite membrane was found. Membranectomy was performed in 37 cases, mostly as a secondary procedure after burr-hole evacuation and closed system drainage. The mortality rate was 6.6% and in the survivors a complete recovery was achieved in 90%. CT monitoring of the diameter of the hematoma and midline shift did not reveal any correlation of size of the hematoma with neurological findings. The indication for membranectomy can, therefore, not be based on radiological findings alone, but on the clinical course of events and with due regard to the CT findings.