Cross-sectional ultrasonic (US) and computed tomographic (CT) scans were obtained to compare their relative accuracies in determining cerebral ventricular size in 20 infants less than one year of age. The goal was to determine whether ultrasound imaging techniques could replace CT in the serial evaluation of the lateral ventricles, particularly in patients with ventricular shunts. The US images were obtained with a servo-controlled real-time sector and trapezoid scanner of the authors' own design. In 85% of the infants, biventricular width by US and CT differed by less than 0.5 cm, and in 95% by less than 1 cm.