OBJECTIVES—Although there is general agreement that surgery is the best treatment for chronic subdural haematoma (CSDH), the extent of the surgical intervention is not well defined. METHODS— The less invasive surgical technique of bedside percutaneous subdural tapping and spontaneous haematoma efflux after twist drill craniostomy under local anaesthesia was prospectively analysed in 118 adult patients, 99 with unilateral and 19 with bilateral CSDH. RESULTS—The mean number of subdural tappings was 3.2. Ninety two of the patients with unilateral CSDH were successfully treated by up to five subdural tappings, 95% of the patients with bilateral CSDH were successfully treated by up to 10 subdural tappings. The mean duration of inpatient treatment was 12 days. In 11 patients (9%) the treatment protocol had to be abandoned because of two acute subdural bleedings, two subdural empyemas, and seven cases of insufficient haematoma efflux and no neurological improvement. The only significant predictor for failure of the described treatment protocol was septation visible on preoperative CT. CONCLUSIONS—The described therapy protocol is—apart from a purely conservative treatment—the least invasive presently available surgical technique for treating chronic subdural haematoma. Its results are comparable with other modern treatment protocols. Thus, it can be recommended in all patients as a first and minimally invasive therapy, especially in patients in a poor general condition. Patients with septation visible on preoperative CT should be excluded from this form of treatment.