The aim of this study was to assess the cost-effectiveness of topiramate vs. no preventive treatment in the UK. Model inputs included baseline migraine frequency, treatment discontinuation and response, preventive and acute medical cost per attack [2005 GBP ( pound)] and gain in health utility. Outcomes included monthly migraines averted, acute and preventive treatment costs and cost per quality-adjusted life year (QALY). Topiramate was associated with 1.8 fewer monthly migraines and a QALY gain of 0.0384. The incremental cost of topiramate vs. no preventive treatment was about 10 UK pounds per migraine averted and 5700 UK pounds per QALY. Results are sensitive to baseline monthly migraine frequency, triptan use rate and the gain in utility. Incorporating savings from reduced work loss (about 36 UK pounds per month) suggests that topiramate would be cost saving compared with no preventive treatment. This analysis suggests that topiramate is a cost-effective treatment for migraine prevention compared with no preventive treatment.