Eighteen macrocephalic children with enlargement of the subarachnoid space (ESAS), with or without mild ventricular dilatation, were followed prospectively to a mean age of 56 months. All were born at term, with uneventful neonatal period and negative tests for congenital infections. There were 17 boys and 1 girl and the mean follow-up period was 46 months (8-58 months). The initial neurologic evaluation, between ages of 2 to 33 months, disclosed abnormalities in 2 cases. At the follow-up one was still abnormal and the other had a normal neurological examination. Another child, who had a normal neurological examination at the age of 5 months, at the age of 7 years and 7 months had an IQ of 77. Thus the abnormality rate at follow-up was 11%. The OFC returned to the normal range in 45% of the children at the follow-up period. There were no cases of intracranial hypertension. One infant had subdural taps performed at the age of 13 months that disclosed a fluid with the same characteristics as the CSF. All the children had a CT-scan performed at the beginning of the study that revealed a large subarachnoid space; in 77% it was associated with mild ventricular dilatation. Eleven had CT-scans repeated, during the study period, which showed resolution of the process in 3 cases, improvement in 2, and unchanged in 6. We conclude that enlargement of the subarachnoid space in macrocephalic children is often a benign entity. ESAS and macrocephaly will still be present in the majority of children in the long-term follow-up.