A new study from Boston University researchers estimates that roughly 75% of deceased NFL players had at least some degree of chronic traumatic encephalopathy, the degenerative brain disease tied to repeated head trauma.
The research examined more than 2,300 deceased former players aged 80 or older who died between 2008 and 2023. Of those, nearly 400 had donated their brains for study, and 93.5% of those donors were diagnosed with CTE.
Researchers noted that former players with clear cognitive symptoms while alive were roughly five times more likely to have donated their brains than those without such symptoms, a gap that likely skews the donor-based diagnosis rate higher than the full population figure. Donors also died younger on average, at 67 years old, compared to nearly 75 for the broader group studied.
CTE cannot be diagnosed in a living person. It is identified after death across four stages, with stage 4 representing the most severe form of the disease. The study cautioned that “many cases may have been early stage at the time of death and possibly symptom free.”
Researchers also estimated that 27.2% of the players studied had a history of all-cause dementia during their lifetimes, though the study did not establish that CTE was the cause.
The findings follow an August study estimating that at least one in four people who have played in the NFL might expect to develop CTE at some point in their lives.
Symptoms associated with CTE include memory loss, mood swings and erratic behavior. The disease was first identified in boxers but has become closely linked to football because of the repeated head impacts players absorb on nearly every snap. It has also been documented in athletes who played hockey, rugby and other contact sports.
The disease’s connection to football entered public view after players including Junior Seau, Mike Webster and Frank Gifford were diagnosed with CTE after their deaths. Webster became known as “Patient Zero” after Dr. Bennet Omalu examined his brain and became the first to diagnose an NFL player with the disease, a finding that triggered the league’s ongoing reckoning with concussions.
That reckoning continues on the field. The NFL recorded 168 documented in-game concussions during the 2025 season, a 30% increase from the 129 recorded in 2024. The league logged a total of 538 evaluations and 26 medical timeouts over the season.
