Long-term valproate treatment is associated with polycystic ovaries and endocrine disorders in women with epilepsy. The mechanisms responsible for these effects are unknown, but both the epilepsy itself and the drug per se may be of importance. The aim of this study was to investigate possible effects of the drug on gonadal structure and function in animals with no epileptic disorders. Three groups, each of 15 female Wistar rats, were fed perorally with a valproate mixture (50 mg / kg or 200 mg / kg) or control solution once daily for 90 days, giving mean valproate concentrations within the normal human range. A significant, 20% increase in ovary weight was found in both low- (P = 0.027) and high- (P < 0.001) dose animals together with a significantly increased number of ovarian follicular cysts. Mean serum testosterone concentration was significantly reduced in both low- and high-dose animals. There was a non-significant trend towards reduced estrogen levels, while progesterone levels were unchanged. Even if the hormonal changes are somewhat different from those in humans, the findings demonstrate that changes in gonadal structure and endocrine function also occur in intact animals indicating a drug-specific effect. Our findings encourages further studies using animal models to elucidate possible mechanisms involved in the endocrine side-effects of antiepileptic drugs.