Summary: Of the 605 patients seen since 1973, 336 patients have been treated with sodium valproate (VPA) alone or in combination with drugs other than carbamazepine (CBZ). Of these 336, 240 have been on monotherapy, of whom 200 are seizure-free. Follow up has been longer than 3 years in 78%. Complete control of seizures has been achieved in more than 80% of patients with absence, myoclonic, and primary tonic-clonic seizures, in 72% of those with photosenstivie epilepsy including eyelid myoclonia, and in 47% of partial epilepsies, for which carbamazepine was the initial drug of choice. Only 21% of those with myoclonic astatic epilepsy have become free from seizures. At first VPA was given twice daily, but in recent years it was given once daily, as this was more effective. Reasons for failure of VPA therapy are given. Side effects in 436 patients (100 more patients were added for this assessment only) were uncommon, though where they did occur, weight increase was the most frequent. Platelets were reduced without clinical problems. There were no severe hepatic disorders. Serum levels were assessed in seizure-free patients, and the optimum level was between 60 and 120 mg/L (most patients received between 20 and 30 mg/kg). VPA was given during 30 pregnancies, and there was no evidence of teratogenicity on monotherapy. VPA is most effective in primary generalized epilepsy, especially if given as the sole antiepileptic drug. If the daily dose does not exceed 40 mg/kg or 2.5 g, it is singularly free from serious side effects.