Purpose Despite the common occurrence of intellectualdisability (ID) in people with epilepsy, most studies of the cost of epilepsy have focussed primarily or exclusively on people without ID. This paper estimates the costs of supporting people with epilepsy and ID. Methods Prospective resource use and outcome data were collected on 91 participants from the east of England for seven months. Multivariate analysis was used to investigate the relationship between costs and patient and healthcare provider characteristics. Results Mean health care costs relating to epilepsy or ID were £2800 (3500 Euros, 5200 USD) p.a. Modelling suggests costs are lower for patients with more severe ID (p = 0.014); and higher for patients managed by a consultant neurologist (p = 0.037). Discussion Our findings support limited evidence from the literature of increased epilepsycosts in people with ID. Patterns of expenditure suggest clinical variation in the treatment of epilepsy according to the severity of ID, particularly in the absence of management by a consultant neurologist.