The incidence of shunt infections and possible risk factors was investigated by chart analysis. From 1986 to 1989 350 shunt procedures were performed including 273 ventriculoperitoneal shunts and 75 ventriculoatrial shunts. Twenty-eight infectious episodes (8%) occurred in 25 patients during a median follow-up time of 20 months. For 204 patients the follow-up time could be prolonged until September 1992. In these patients no infectious episodes occurred in the extended observation period. In 24 cases (85.7%) a causative organism could be isolated. The infecting organisms were gram-positive cocci in 22 cases (78.6%) and gram-negative bacilli in two cases. The main signs and symptoms were fever, shunt malfunction and meningeal irritation, and with VP-shunts only, abdominal pain. Twenty-four infectious episodes were treated with antibiotics and immediate removal of the shunt. The remaining were managed with antibiotics only. The risk for shunt infection did not correlate with age or sex of patients, nor with the etiology of hydrocephalus, type of shunt implanted or perioperative antibiotic prophylaxis. However, a trend showing a higher risk for shunt infections with prolonged operation time was noticed. The infection rate was 13.6% for an operation lasting more than 90 minutes versus 5.2% for procedures of less than 30 minutes duration.