Fourteen patients with juvenile myoclonic epilepsy (JME) were treated with a single low dose of a sustained-release preparation of sodium valproate (VPA, 500 mg daily). The mean age of the onset of the low dose treatment was 19.2 years (range 14-26). Before this treatment, six patients had been treated with high dose VPA for a period of more than 2 years, three patients for 1 to 2 years, three patients less than 1 year and two patients initiated the treatment from the beginning with a low dose. The mean duration of low dose treatment is 35.6 months (range 25-59 months). (All patients are still under medication). Generalized tonic-clonic and absence seizures were controlled in all patients. Myoclonic jerks relapsed only in one patient, a young mother who was looking after her newly born baby and was deprived of sleep. No adverse reactions have been reported. We suggest that JME patients can effectively be treated with single low VPA dose (500 mg daily), while at the same time seizure precipitating factors, such as sleep deprivation and alcohol ingestion, should be avoided.