This cross-sectional study was planned to study the blood ammonia levels in epileptic children on 2 dose ranges of valproic acid monotherapy. A total of 60 epileptic children aged 3 months to 12 years, that were on valproic acid monotherapy for at least 3 months, were enrolled and divided into 2 groups, a low-dose group (dose, 20-39 mg/kg/d [n = 32]) and a high-dose group (dose, 40-60 mg/kg/d [n=31]). Measurements of blood ammonia, serum valproic acid levels, and liver and renal function tests were performed. Blood ammonia levels were significantly higher in the high-dose group (median, 79.2 µg/dL; range, 55.23-114.29 µg/dL) as compared with the low-dose group (median, 47.2 µg/dL; range, 20.62-73.25 µg/dL). Blood ammonia levels significantly correlated with both the dose (r = .77, P < .001) and serum levels (r = .88, P < .001) of valproic acid. All the children with hyperammonemia were asymptomatic. There were no significant differences in the other biochemical parameters between the 2 groups.