In about seven out of ten people with epilepsy, no cause can be found. Among the rest, the cause may be any one of a number of things that can make a difference in the way the brain works. For example, head injuries or lack of oxygen during birth may damage the delicate electrical system in the brain.

Other causes include brain tumors, genetic conditions (such as tuberous sclerosis) , lead poisoning, problems in development of the brain before birth, and infections like meningitis or encephalitis.

Epilepsy is often thought of as a condition of childhood, but it can develop at any time of life. About 30 percent of the 125,000 new cases every year begin in childhood, particularly in early childhood and around the time of adolescence. Another period of relatively high incidence is in people over the age of 65.