Summary: A simple definition of the treatment gap is the number of people with a condition or disease who need treatment for it but who do not get it. It is an underutilised measure of health care. In epilepsy, it has been estimated by the direct method, during prevalence studies, and indirectly from the amount of antiepileptic drugs consumed in the country and the number of people with active epilepsy. The treatment gap in epilepsy is very high in the developing world. Possible causes of the treatment gap have been listed, but these have not been investigated.