Acquired brain injury may occur through the sudden onset of trauma, infection, lack of oxygen, strokes, and drug use episodes, or through prolonged alcohol or substance abuse, and tumours or degenerative neurological diseases. Two thirds of all people with this disease are over the age of 45. One third of those are over the age of 65, and the largest age group is between 40 and 49. The disease is higher in men than women. Acquired brain injury is any damage to the brain affecting a person physically, emotionally or behaviorally. It can happen at birth or later, from an illness or trauma, and can be called traumatic or nontraumatic, depending on the specific cause.

There could be many possible causes of it including road accidents, assaults, falls and accidents at home or at work, stroke, brain tumor, haemorrhage, or viral infection such as meningitis.