Topiramate has been shown to be effective as a preventive treatment for migraine in three large placebo-controlled, dose-ranging trials. Because the protocols were similar in design using the same primary and secondary endpoints, data from these studies were pooled to evaluate the consistency of efficacy, efficacy by gender and tolerability of topiramate 100 mg/day (n = 386) versus placebo (n = 372). Topiramate was superior to placebo as measured by the reduction in mean monthly migraine frequency, monthly migraine days and monthly migraine duration. The responder rates, defined as at least 50% reduction for the respective parameters, were significantly in favour of topiramate (p < 0.001), for example 46.3% of patients on topiramate achieved at least 50% reduction in monthly migraine period frequency compared with 22.8% on placebo (p < 0.001). Use of medication to treat the acute migraine attack was significantly reduced by topiramate compared with placebo (p < 0.001). The therapeutic effect was consistent throughout the different studies and independent of gender. The most common adverse effect was paraesthesia, mostly of mild-to-moderate severity. The findings confirm that, at a dose of 100 mg/day, topiramate is an effective and well-tolerated drug for migraine prevention.