The long-term efficacy and adverse-event profiles of sodium valproate and carbamazepine in children with newly diagnosed primary generalised or partial epilepsy were compared at 63 outpatient clinics. Children with two or more generalised tonic-clonic or partial seizures in the previous six months were randomised to oral sodium valproate (N = 130) or oral carbamazepine (N = 130) and followed for three years as outpatients. Dosages were increased as needed until seizures were controlled or toxicity developed. Sodium valproate and carbamazepine were equally effective in achieving high levels of seizure control in both primary generalised seizures and partial seizures with or without generalisation. Adverse events were mostly mild, few necessitating drug withdrawal. Those particularly associated with valproate were weight increase, alopecia and appetite increase, and with carbamazepine, rashes, somnolence, diplopia and abnormal gait/ataxia.