In order to analyze the surgical outcome according to clinical characteristics and to evaluate the correlation between clinical improvement and neuroimaging changes, we retrospectively reviewed 32 children who had undergone endoscopic III ventriculostomy (ETV) from February 1994 to May 1998. There were 15 boys and 17 girls, with a mean age of 5.2 years (range: 1 month to 13 years). The etiology of the hydrocephalus was primary aqueductal stenosis in 18 patients, secondary aqueductal stenosis caused by tumors in 5, IV ventricle outlet obstruction in 5, and hydrocephalus associated with meningomyelocele in 4. The mean duration of follow-up was 19.4 months (range 1-50 months). Overall, surgical outcome was regarded as good in 21 of 29 patients. Surgical outcome was poor in patients younger than 1 year (P<0.05). Neuroimaging 1 month after ETV showed a decrease in ventricular size in 11 of the 16 patients with good surgical outcomes. Five showed minimal changes only. In patients with good outcomes, ventricular size tended to decrease as time passed. Resolution of periventricular edema, flow void in the III ventricle on T2-weighted axial images, and cine-MR imaging were sensitive indicators of good outcome. We suggest that ETV be considered as a primary treatment option in patients older than 1 year of age with noncommunicating hydrocephalus. In addition, time factors should be taken into consideration when surgical outcome is judged. Changes in ventricular size could not predict surgical outcome completely in themselves. Therefore, a comprehensive postoperative assessment should be made with the help of T2-weighted MRI and cine-MRI.