A placebo-controlled trial was carried out among 2067 Indonesian neonates to assess the safety of administering one oral 52-mumol (50,000 IU) dose of vitamin A. Infants were assessed for potential acute side-effects before and throughout 48 hours after the dose. The first 965 infants were examined by cranial ultrasound before and at 24 hours after dosing to rule out intracranial haemorrhage and determine the resistive index (RI) of the anterior cerebral artery using duplex Doppler. Groups were comparable at the baseline. A bulging fontanelle occurred in the control and vitamin A groups, respectively, among 2.7% and 4.6% of the infants at 24 hours, and 2.4% and 4.5% of the infants at 48 hours. The groups did not differ in any other sign or symptom assessed. No infant developed intracranial haemorrhage. Mean RI values were normal and not different between groups at baseline or at 24 hours. Mean RI fell during the 24 hours, as normally occurs; the mean decrease was nearly identical in the two groups. A bulging fontanelle was not associated with increased rates of any sign or symptom or with an increase in RI. The 52-mumol dose of oral vitamin A may cause a small increase in intracranial volume in a small proportion of infants, but no increase in intracranial pressure. Acute side-effects following this intervention were rare and mild.