Posttraumatic seizures are relatively common among patients with severe head injuries, with major risk factors being penetrating head wound, hematoma, depressed skull fracture, and, for late seizures, early seizures. Management of late posttraumatic seizures, if they do develop, follows the treatment of patients with epilepsy. Their treatment should be determined by the type of seizure (i.e., partial or generalized) and the individual responsiveness of the patient to drug therapy. Prophylactic administration of antiepileptic drugs to prevent posttraumatic epilepsy has been frequently tried. The data supports a short-term but not a long-term effect of the most commonly used drug, phenytoin. A decision of whether to use prophylaxis, with what, and for how long needs to consider the likely benefit (i.e., the chance of seizures if untreated and the likelihood that the proposed treatment will substantially reduce that chance) and risk (i.e., medical or behavioral adverse effects) of this treatment strategy.