Epidemiologic studies have shown no increased risk of epilepsy after mild head injury (i.e., brief loss of consciousness or amnesia). Twelve cases of new-onset epilepsy occurring less than or equal to 6 months after mild head injury were identified. None of the patients had other risk factors for epilepsy. There was no loss of consciousness in three cases; in the remaining nine, the duration of posttraumatic unconsciousness was less than or equal to 10 min, Nine patients had epileptiform activity or video-EEG documented epileptic seizures; two other patients had focal slowing on the EEG. Eight patients have medically refractory epilepsy, probably reflecting the selection bias. These cases suggest that in certain instances mild head trauma may cause epilepsy.