The authors examined the incidence of widened subarachnoid spaces (SAS) among 75 infants with birthweights less than or equal to 1250g, and their significance in developmental outcome. Nine of 30 infants with gestations less than or equal to 27 weeks had widened SAS in their pre-discharge ultrasound scans. Three of the nine, including two with periventricular leukomalacia (PVL), had late-onset ventricular enlargement, unrelated to intraventricular haemorrhage (IVH): all three were developmentally impaired. The other six infants without ventricular enlargement developed normally, including one with IVH. Five of the remaining 21 infants with gestations less than or equal to 27 weeks and without widened SAS were developmentally impaired. Widened SAS was not associated with a significantly increased risk of developmental impairment; ventricular enlargement and PVL were the only significant factors. The authors conclude that an isolated finding of widened SAS is not predictive of impairment in immature infants.