Between January, 1984, and December, 1990, a total of 85 patients have undergone stereotactic third ventriculostomy (TV) at the Mayo Clinic. Sixty-one patients (74%) presented with mass lesions in the region of the posterior third ventricle, aqueduct of Sylvius or fourth ventricle. Twenty-four patients (26%) presented with non-tumoral, adult/adolescent-onset aqueductal stenosis. Follow-up was available for all 85 patients and ranged from 1 to 66 months (mean 25 months). Follow-up revealed initial patency in 84 patients. Eleven patients (13%) ultimately required extracranial shunting for persistent symptomatic hydrocephalus. Two patients underwent revision of their TV. Twenty-seven patients had been previously shunted. Of these, 23 (85%) have remained asymptomatic after TV without the need for further shunting. Stereotactic TV is a safe and effective way of re-establishing normal cerebrospinal fluid flow dynamics in selected cases of obstructive hydrocephalus.