Among all patients with severe head trauma who receive medical attention, about 12% develop posttraumatic seizures; this rate is more than 50% for those with penetrating head injuries. Posttraumatic seizures are defined as early (occurring in the first week after injury) or late (longer than 7 days after injury) (Table 191.1). Seizure activity in the early posttraumatic period following head injury may cause secondary brain damage because of increased metabolic demands, raised intracranial pressure, and excess neurotransmitter release. The development of seizures complicates the acute management and rehabilitation of head-injured patients. These seizures can be physically and psychologically debilitating. However, early seizure development does not affect long-term patient outcomes.