Real-time ultrasound studies of the head were performed on 96 infants weighing 1500 g or less. This population represented all such infants admitted within the first 72 hours of life to a neonatal intensive care unit over a 9-month period. Intracranial subependymal/intraventricular hemorrhage occurred in 22 (23%) of the infants. Of these 13 (59%) developed ventricular enlargement. Four other infants, in whom hemorrhage was not identified, also developed ventricular enlargement. When it occurred, the ventricular enlargement developed within 2 weeks of the hemorrhage in 77% of cases. It reached its maximum size within 2 weeks in 65% of cases. In 9 of 16 cases the maximal ventricular enlargement was categorized as mild. Spontaneous arrest or resolution of the ventriculomegaly occurred in all but two cases, who required shunting. Clot resolution was slow. It was complete at 3 weeks in only 5 of 18 cases.