We report the results of a randomized, double-blind, placebo-controlled study to determine whether phenytoin administered soon after a head injury lessens the incidence of late post-traumatic epilepsy in children. 41 patients were randomized into either a phenytoin or placebo group and followed for 18 months. The patients were administered phenytoin or placebo intravenously or intramuscularly within 24 h of hospital admission. The patients were parenterally administered phenytoin or placebo until oral doses could be tolerated. There was no significant difference in the percentage of children having seizures in the treated and placebo groups (p = 0.25).