The data of 48 patients with a subdural empyema, treated in the period 1946-1980, have been reviewed in order to evaluate factors that influenced the outcome. A delay in diagnosis and surgical treatment, plus a severe disturbance of consciousness at the moment of surgery, all had a negative bearing on the subsequent outcome. The mode of operation also had an influence on the outcome in this series. In those patients with a severely disturbed level of consciousness at the time of surgery, the outcome was more favourable if multiple burr-holes were performed rather than a craniotomy. In patients with a minor disturbance of consciousness, however, this difference was not apparent.