We assessed the value of valproate in the prevention of recurrent attacks of absence status in 25 patients. Eighteen patients had primary generalized epilepsy with a mean frequency of attacks of absence status of 5.7 per year. After a mean follow-up period of 4.4 years, the attack frequency was reduced to 0.6 per year (p less than 0.0005); 14 patients had no recurrence, 3 had rare attacks with noncompliance, and 1 had an incomplete response probably due to gastrointestinal intolerance. Patients with evidence of generalized cerebral damage (n = 2) or with EEG evidence of focalization (n = 5) did not respond as favorably. Valproate is the drug of choice for the prevention of recurrence of absence status. Moreover, the response can be predicted on the basis of the electroclinical subtype of absence status.