Despite the high incidence of chronic subdural haematoma (SDH), to date relatively few authors have undertaken a systematic analysis of the results attained following burr-hole craniostomy and closed-system drainage on the basis of a study involving a large patient population defined according to clear-cut criteria. Between 1980 and 1993, surgery was performed on 212 patients with a chronic SDH. In a retrospective study, the condition of each patient was assessed at the time of admission on the basis of the Bender Scale and the results 4 weeks after discharge were classified according to the Glasgow Outcome Scale (GOS). At admission, 165 patients (78%) were in a satisfactory condition (Stage 1 or 2); 47 (22%) were at Stage 3 or 4, i.e. stuporous or comatose. Nine (4%) of the patients died; none of these deaths was attributable to the operation. In addition to significant extracerebral disease (2.4%), CT revealed ischaemic cerebral infarctions in three patients (1.4%) after removal of the SDH. The operative morbidity was 4.2%. In 22% of the patients, surgical intervention was required to remove a recurring SDH. In 90% of the patients, the results achieved could be graded as 'very good' or 'good' (GOS 1 or 2). The results were related to the condition at admission (p < 0.001) and the patient's age (p < 0.05). Factors that did not have a significant effect on the outcome included whether the SDH formation was bilateral or unilateral, the extent of neomembranous organization of the haematoma, and the amount of primary cerebral expansion following decompression. We were able to confirm the results of previous studies that the method used is a highly effective treatment, with a low incidence of complications.