OBJECTIVES - To assess the efficacy of topiramate in the treatment of idiopathic intracranial hypertension (IIH) and to compare it with acetazolamide. METHODS - Fourty patients diagnosed as IIH and randomly assigned to treatment with either acetazolamide or topiramate were assessed prospectively. Improvement in the visual fields at the end of third, sixth and twelfth months were taken into consideration. RESULTS - The demographic, clinical features and the cerebrospinal fluid (CSF) pressure of the two treatment groups were similar at the beginning of the study. When the follow-up visual field grades were compared with the visual field grades at the beginning of the study in each group a statistically significant improvement was detected with both drugs. When the results of the two treatment groups were compared with each other no statistically significant difference was present. Prominent weight loss was recorded in the topiramate group. CONCLUSIONS - Topiramate seems to be effective in the treatment of IIH. Weight reduction as well as the reduction of the CSF formation is the possible mechanism of action.