OBJECTIVES: With about 33 million children affected worldwide, epilepsy is a common neurological disorder creating significant socio-economic costs. This study aims to estimate the additional costs or savings generated by the introduction of levetiracetam for refractory partial onset seizure (POS) in paediatric patients in the UK. METHODS: A budget impact model was built from the UK NHS perspective, for a 5-year time period. Levetiracetam adjunctive therapy was compared with standard treatments (ST): lamotrigine, oxcarbazepine, valproic acid, carbamazepine and topiramate. Epidemiological paediatric population data such as prevalence of refractory POS cases were obtained from the published literature and combined with UK population projections for 2005 from official statistics sources. Patients on levetiracetam were divided into three groups: new, existing and withdrawing patients to reflect the progressive adoption of the treatment. The cost of medications and hospitalizations were included and expressed in 2005 UK£. RESULTS: During the first year, the number of paediatric patients with refractory POS was estimated to be 7,205. The annual cost per patient for current ST was £1,593, resulting in a total budget of £11.5 million. Within the next five years, the number of paediatric patients will increase to 7,267, resulting in a total budget of £11.6 million. Adding levetiracetam to ST increased the yearly drug costs by £1,089 per patient. This additional cost was partly offset by lower hospitalization costs (£332 and £815 per patient for levetiracetam and ST respectively). Introducing levetiracetam resulted in a budget increase to £11.7 million (+1.8% compared to current budget) during the first year and £12.1 million (+4.7%) over the next five years. CONCLUSION: Levetiracetam as adjunctive therapy in paediatric patients with refractory POS is predicted to result in a modest increase in UK NHS paediatric epilepsy expenditure of 4.7% within a 5-year time period.