About 25% of seizures in the neonatal period have causes other than asphyxia, ischaemia or intracranial bleeding. Among these are primary genetic epileptic encephalopathies with sometimes poor prognosis and high mortality. In addition, some forms of neonatal infant seizures are due to inborn errors of metabolism that do not respond to common AEDs, but are amenable to specific treatment. In this situation, early recognition can allow seizure control and will prevent neurological deterioration and long-term sequelae. We review the group of inborn errors of metabolism that lead to newborn/infant seizures and epilepsy, of which the treatment with cofactors is very different to that used in typical epilepsy management.