Endoscopic third ventriculostomy (ETV) has gained widespread acceptance as an effective way to manage hydrocephalus in selected patients. To determine which patient groups have the highest chance of successful ETV, a retrospective case review was performed. From June 1992 to December 1996, 97 patients underwent a total of 98 ETVs at our institution. There were 59 males and 38 females with a mean age of 8.1 years (range 1 day to 29.5 years). Twenty-six of 98 procedures (26%) were abandoned due to either unfavorable anatomy, inability to perform a cisternostomy, or hemorrhage. Follow-up data was available in 92 patients for a mean of 24.2 months. The rate of successful ETV in 71 patients, with either complete shunt avoidance or removal, varied widely by diagnosis and patient age. The highest success rates were achieved in patients with aqueductal stenosis, tectal plate tumor, myelomeningocele and posterior fossa tumor. Complications included one transient herniation syndrome, one basilar artery perforation, 2 cases of ventriculitis, one transient decrease in level of consciousness, and one transient hemiparesis. We feel these results support the continued use of ETV in only carefully selected patients with hydrocephalus.