Nonalcoholic fatty liver disease was defined recently as another symptom of insulin resistance. Continuous therapy with valproate can result in increased body weight and insulin resistance, but no data are yet available on a possible relationship between valproate and nonalcoholic fatty liver disease. We here demonstrate in abdominal ultrasound investigations that characteristics of fatty liver disease were present in 61% of valproate‐treated patients as compared with 23% receiving carbamazepine therapy. Ann Neurol 2004