There is no single definition of medically refractory epilepsy, and different definitions may be appropriate depending on the form of epilepsy or on the purposes for which the definition is being used. The natural history of the specific form of epilepsy must be accurately characterized to facilitate a meaningful definition of refractory for that form of epilepsy and thereby allow identification as soon as possible in the course of the disorder. Long-term follow-up after appearance of intractable epilepsy (as determined by a variety of definitions) would provide helpful information necessary for refining meaningful definitions of intractability.