The occurrence of post-traumatic epilepsy (PTE) was studied in 164 consecutive closed head injury patients, each of whom had been unconscious and amnestic for at least one hour. The overall incidence of PTE was found to be 25%, significantly higher than previously reported. Analysis of data revealed PTE was not related to the presence or absence of a hematoma, but rather to the duration of the coma. The incidence of PTE was found to be 35% among patients comatose for three weeks or more.