Follow-up examination was carried out in 37 children who had been hypoglycaemic during the neonatal period. Mean age was 3 1/2 years. Five out of 7 children with asymptomatic hypoglycaemia neonatally were completely normal, while minimal brain dysfunction was evident in one, and another child showed pathological EEG. Symptomatic, transient hypoglycaemia seemed to carry a poor prognosis as only one out of 9 individuals was normal. Four patients in this group had convulsions after the neonatal period; two of these had recurrence of hypoglycaemia. One had infantile spasms and was severely mentally retarded with spastic diplegia and epilepsy. One girl was blind due to optic nerve atrophy. Four cases of cerebral palsy were detected in this group. Among 21 cases of secondary hypoglycaemia there were no cases of serious neurological sequelae. It is reasonable to assume that neonatal hypoglycaemia is an important prognostic factor. The deleterious effect on the CNS seems to be related to the duration and severity of the hypoglycaemia.