Traumatic acute subdural haematoma is one of the most lethal of all head injuries: the mortality rate is reported to be between 50 and 90%. We reviewed the clinical records of 1688 head injured patients admitted to the Department of Neurosurgery at C.T.O. hospital between 1982 and 1992. In 127 cases (7,5%) CTscan on admission showed acute subdural haematoma requiring surgery because the midline shift was greater than 5 mm. The overall mortality rate was 57% and 23% had functional recovery. The following variables were assessed with regard to morbidity and mortality: mechanism of injury, age, neurological presentation, time delay from injury to intervention, CTscan finding on admission. GCS and CTscan findings were found to be the most important prognostic variable. Timing of operative intervention for clot removal with regard to outcome was not statistically significant. But no conclusions regarding the importance of early haematoma evacuation can be drawn from such an oversimplifying statement, because it does not take into account factors like rapidity of haematoma development and related brain decompensation as well as additional direct brain lesions. The results of this study suggest that the extent of primary brain injury underlying the subdural haematoma is the most important factor affecting outcome.