Within the period from 1981 to 1986 a total of 65 patients with 74 (9 bilateral) chronic subdural haematomas (CSH) were operated on. First symptoms, preceding diseases, accompanying factors and neurological findings were listed and evaluated retrospectively. Preoperative CT criteria and postoperative CT controls of the course were put in relation to the clinical development of the findings obtained with different surgical techniques. The comparison of borehole trepanation (37 haematomas) and large craniotomy (37 heamatomas) shows advantages with respect to the retrogression of the haematomas (CT), the postoperative clinical course and the complications in favour of the patients subjected to borehole trepanation.