A total of 228 low birth weight (less than 1750 g), mechanically ventilated infants with and without periventricular-intraventricular hemorrhage were examined at 18 months corrected age to assess the relationship between cranial ultrasonographic findings and specific motor abnormalities. All infants were previously enrolled in a double-blind, randomized, prospective clinical trial of phenobarbital prophylaxis against periventricular-intraventricular hemorrhage. Ultrasonographic abnormalities on the scans performed between 7 and 13 days of life were categorized as germinal matrix hemorrhage, lateral ventricular hemorrhage, parenchymal hemorrhage, ventriculomegaly, and any hemorrhage. Regardless of anatomical location, periventricular-intraventricular hemorrhage was associated with an increased risk for developing motor abnormalities. Hypertonia and hyperreflexia/ankle clonus were most common. No abnormal motor findings distinguished unilateral from bilateral germinal matrix hemorrhage and lateral ventricular hemorrhage or between phenobarbital and placebo treatment. None of the 5 infants with parenchymal hemorrhage had spastic cerebral palsy. Ventriculomegaly was associated with a fivefold increase in risk for spastic cerebral palsy and delayed walking and a threefold increase for hypertonia and hyperreflexia/clonus. The results suggest that ventriculomegaly, observed even as early as the first week of life, might be a significant antecedent of later motor abnormalities among the survivors of periventricular-intraventricular hemorrhage.