OBJECTIVES: Epilepsy is a brain disorder which is characterized by recurrent unprovoked seizures. The outward effect of seizures can be as dramatic as a wild trashing movement or as mild as a brief loss of awareness. To reduce frequency and severity of seizures, antiepileptic drugs are potentially an effective treatment for patients with epilepsy. However, side-effects are common. The negative consequences of side-effects can lead to treatment ranging from minor care to very expensive hospitalization. This cost analysis has been conducted to provide insight into the costs of side-effects due to antiepileptic drugs in The Netherlands from a societal perspective. METHODS: Health care, patient and family and other use of resources for five different categories of side-effects were measured by means of a questionnaire. Respondents were patients with epilepsy who experienced at least one side-effect due to antiepileptic treatment in the last 12 months. RESULTS: Based on data from 203 chronic epilepsy patients, the overall societal costs of common side-effects in 2012 are estimated to be €20,751 (CI: 15,049-27,196) per patient per year in the base case analysis. These societal costs exist of: mean health care costs (€4,458), mean patient and family costs (i.e. informal care and out of pocket expenses) (€10,526) and mean other costs (i.e. productivity and daily routine losses) (€5,761). Examining the different categories of side-effects separately, ranging from the most to the least expensive category, the cost estimates were as follows: other side-effects (€13,228), behavioral side-effects (€9,689), general health side-effects (€7,454), cognitive side-effects (€7,285) and cosmetic side-effects (€2,845) per patient per year. Subgroup analyses showed significant differences in costs between patients using monotherapy and those using polytherapy when looking at cognitive and cosmetic side-effects. CONCLUSIONS: These estimates should be considered in the overall assessment of the economic impact of a pharmacotherapy.