Screening cranial ultrasounds were performed on 115 very low birthweight infants during the first week of life. Fourteen infants (12%) developed changes of periventricular leukomalacia. All 14 weighted 1100 g or less at birth. Eight infants' initial studies were normal, four had intraventricular hemorrhage, and two had periventricular echo densities. Cystic periventricular leukomalacia developed between 17 and 104 days of age and occurred later in those infants whose initial study was normal. There were tone abnormalities in 11 of the 12 infants who received developmental follow-up. Severe cognitive delays were common in the older infants. This study demonstrates the need for late ultrasound screening even in the presence of initial normal ultrasound examinations.