Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease linked to repeated trauma to the head. The encephalopathy symptoms can include behavioral problems, mood problems, and problems with thinking. The disease often gets worse over time and can result in dementia. It is unclear if the risk of suicide is altered.

Most documented cases have occurred in athletes involved in striking-based combat sports, such as boxing, kickboxing, mixed martial arts, and Muay Thai—hence its original name dementia pugilistica (Latin for "fistfighter's dementia")—and contact sports such as American football, Australian rules football, professional wrestling, ice hockey, rugby, and association football (soccer), in semi-contact sports such as baseball and basketball, and military combat arms occupations. Other risk factors include being in the military, prior domestic violence, and repeated banging of the head. The exact amount of trauma required for the condition to occur is unknown, and as of 2022 definitive diagnosis can only occur at autopsy. The disease is classified as a tauopathy.

There is no specific treatment for the disease. Rates of CTE have been found to be about 30% among those with a history of multiple head injuries; however, population rates are unclear. Research in brain damage as a result of repeated head injuries began in the 1920s, at which time the condition was known as dementia pugilistica or "fistfighter's dementia", "boxer's madness", or "punch drunk syndrome". It has been proposed that the rules of some sports be changed as a means of prevention.