A retrospective analysis of US findings was performed in 18 newborns and infants with obstructive hydrocephalus. The purpose was to determine the most precise secion of the US study in evaluating the level and cause of obstruction and to determine whether US imaging can replace CT in the evaluation of hydrocephalus. Among 18 cases of obstructive hydrocephalus, the most common obstructive level was the foramen Monro caused by intraventricular hematoma. The most precise section of the US study in evaluation ofhydrocephalus was the sagittal scan. In aqueductal stenosis, the US sagittal scan was more precise than the CT scan regarding the anatomic realtionship of obstruction. The results suggest that US is a sufficient diagnostic tool for evaluation of hydrocephalus in newborns and infants and CT should be performed only in selected cases.