The brains of 158 consecutively admitted very preterm infants were repeatedly examined with real time ultrasound. Abnormalities, most commonly periventricular haemorrhage, were detected in 79 (50%). The 109 infants who survived were followed up until they were 16-23 months old. Major or minor neurological or developmental sequelae were found in 5 of 62 infants (8%) with normal ultrasound scans and in an identical proportion, 2 of 25 infants (8%), with uncomplicated periventricular haemorrhage. By contrast, 15 of 21 infants (71%) whose ventricles became enlarged (with or without periventricular haemorrhage) had abnormalities at follow up. The proportion with sequelae depended on the cause and extent of the enlargement. Three of 8 infants (38%) with mild (usually transient) ventricular distension had sequelae, compared with 3 of 4 (75%) with hydrocephalus and 9 of 9 (100%) with cerebral atrophy (2 of whom also had hydrocephalus). Adverse neurodevelopmental sequelae at follow up appeared more often to be attributable to cerebral ischaemia and infarction than to periventricular haemorrhage.