Post-concussion synrome, also known as postconcussive syndrome or PCS, is a set of symptoms that a person may experience for weeks, months, or occasionally years after a concussion–a mild form of traumatic brain injury (abbreviated TBI). PCS may also occur in moderate and severe cases of traumatic brain injury. Symptoms of PCS, which is the most common entity to be diagnosed in people who have suffered TBI, may occur in 38–80% of mild head injuries. A diagnosis may be made when symptoms resulting from concussion last for more than three months after the injury, or it may be made starting within a week or ten days of trauma. In late, persistent, or prolonged PCS (PPCS), symptoms last for over six months, or by other standards, three.