In a prospective study 144 adult patients with chronic subdural hematomas were randomly divided into three treatment groups after burr-hole evacuation. The two commonly used procedures (external closed system drainage and aspiration and irrigation without any drainage) were compared to a modified technique: permanent subdural drain with subcutaneous reservoir. After the hematoma was washed out with saline solution, a silicon catheter with multiple perforations was introduced into the subdural cavity and connected to a Rickham reservoir, fixed in the frontoparietal burr hole. In patients who showed secondary deterioration or enlargement of the residual hematoma as proven by computed tomographic scan, the reservoir was punctured and the subdural fluid aspirated. The great advantage of this method is that it is practicable at the bedside as well as in the outpatient department, thus making it possible to reduce the number of additional operations. The incidence of symptomatic residual or recurrent hematoma was similar in all three groups. The reoperation rate was 4-fold greater in the groups treated with conventional therapy, when compared to the group with the implanted system. At the same time there was no indication that the implantation of the drain was less safe, as judged by the incidence of seizures and infections.