PURPOSE: Parents frequently report increased sleep duration in their children during treatment with valproic acid (VPA). We assessed sleep duration and sleep behavior before and after tapering VPA in children treated for more than 6 months. METHODS: Sleep variables were assessed by questionnaire, diary, and actigraphy (for 7 consecutive days and nights) before and 8-12 weeks after termination of VPA. RESULTS: Forty-six children (age range 1.7-17.4 years) completed the study. The questionnaire data showed no significant difference in bed and wake time, duration of sleep, and time to fall asleep before and after ending VPA treatment, although some qualitative measures on daytime sleepiness improved after tapering VPA. The actigraphy data revealed that the average sleep amount without VPA was reduced in 33 children (9 of them >30 min) and longer in 13 children (1 of them >30 min). The mean Assumed Sleep Time per Day decreased by 15.2 min or 9.5 min when the physiologic decrease of sleep duration within 0.3 years was considered. Also mean Actual Sleep Time per Day was significantly reduced after VPA termination (-15.2 min; after correction -10.7 min). The reduction was only significant in children older than age 6 years. DISCUSSION: Termination of VPA after long-term treatment leads to a significant reduction of sleep duration in children older than 6 years of age. The change was small in the majority, but considerable in a subgroup of children.