Of 148 patients with infratentorial brain tumours which were operated upon during a 5 year period, 59 patients had associated obstructive hydrocephalus, as evidenced by preoperative CT scan. External ventricular drainage was performed in these cases at time of surgery. CSF drainage was continued in the postoperative period for a mean of 2.3 (+/- 1.6) days. Only 6 of these 59 patients (10%) required a subsequent indwelling shunt. The infection rate was 10% and the total mortality was 8%. Perioperative ventricular drainage during and following the removal of posterior fossa tumours causing hydrocephalus provides an effective alternative to the preoperative placement of an indwelling shunt. Problems of shunt dysfunction, tumour seeding and upward herniation are thereby avoided. Postoperative ICP monitoring and drainage of blood and debris laden CSF is performed, increasing the safety of the postoperative period and possibly reducing the incidence of aseptic meningitis and postoperative shunt requirement.