The association of cerebral ultrasound images and developmental outcome at age 3 1/2 years was studied in 50 preterm infants (mean gestational age 31 weeks, mean birthweight 1450 g). 25 children had normal neonatal scans and 25 had abnormal neonatal scans; 11 without and 14 with ventricular dilatation. At one year a repeat scan was done and neurodevelopmental outcome was assessed. Follow-up results at 3 1/2 years stress the importance of long-term follow-up: at one year four of the 50 children had developmental deficits, at 3 1/2 years 13 had such deficits. At 3 1/2 years the risk of neurodevelopmental deficits was extremely high for children with persistent haemorrhagic and/or atrophic ventricular dilatation. There was significant over-representation of children with developmental deficits in the group with abnormal scans, both neonatally and at one year. The incidence of cerebral palsy was high in the group with large haemorrhages extending into the parenchyma and/or periventricular leucomalacia. In the group with periventricular leucomalacia there was also a greater risk of mental retardation with severe behavioural problems. Follow-up at a later age than 3 1/2 years will be necessary to determine the effects on the motor, intellectual and emotional development of these children.