For roughly two decades, scientists have linked chronic traumatic encephalopathy (CTE) to football, and hundreds of deceased former players have received a post‑mortem diagnosis. This has left a pressing question: what proportion of NFL athletes will develop the disease?
Recent analysis indicates that at least 25 % of everyone who has played in the NFL could eventually develop CTE, based on a review of hundreds of cases from the past six years.
The study examined all former NFL players who died between 2016 and 2021—a total of 878 individuals spanning ages from their twenties to eighties, with most falling in the middle range.
The analysis showed that 215 of those 878 players—about 24.5 %—had CTE.
The true figure may be higher, since the 25 % estimate excludes the 643 brains that were not tested; many of those could also have CTE.
CTE is a progressive brain disorder resulting from repeated head trauma, and a definitive diagnosis can only be made posthumously.
In individuals without a history of repetitive head impacts, the occurrence of CTE is virtually nonexistent.
Applying the study’s rate to the current NFL—1,696 players on active 32‑team rosters, excluding practice‑squad and injured reserve members—suggests that at least 400 athletes could eventually develop CTE.
Experts characterize this prevalence as an occupational hazard unlike most others seen in American workplaces.
“Workers exposed to high levels of asbestos suffer elevated lung‑disease rates, and long‑term coal miners face a high risk of black lung,” said David Michaels, former OSHA chief under the Obama administration and now a professor at George Washington University’s School of Public Health.
“But I have never encountered a comparable neurodegenerative disease.”
CTE was first identified in boxers almost a hundred years ago, originally called dementia pugilistica. Symptoms include memory loss, confusion, mood swings, impaired executive function, and impulsive or addictive behaviors.
Today, CTE is most often linked to football, yet it has also been detected in athletes from hockey, rugby, soccer, wrestling, and bobsleigh who experience repeated head impacts. Military personnel exposed to artillery blasts show similar susceptibility.
For years the NFL minimized the dangers of repetitive head trauma, claiming insufficient knowledge about CTE to assess its risks, origins, or frequency. This uncertainty has hampered action, and researchers still cannot explain why some athletes avoid CTE despite long careers while others develop severe disease early in life.
However, the reported prevalence is difficult to overlook. This study comes from neuropathologists and scientists primarily affiliated with Mass General Brigham, Boston University, and the UNITE Brain Bank—groups that have driven CTE research and processed most donated athlete brains over the last twenty years.
The authors, whose work appeared Tuesday in The BMJ, plan to release a follow‑up paper estimating the overall CTE rate among all NFL players at death.
Estimating this figure is challenging due to many unknowns, but researchers agree that CTE is preventable.
“We understand the cause,” said Dr. Daniel Daneshvar, study lead author, chief of brain‑injury rehabilitation at Spaulding Rehabilitation Hospital, and associate professor at Harvard Medical School. “It is a neurodegenerative disease whose risk we fully control; grasping its magnitude is essential to reducing that risk.”
Dr. Daneshvar noted that lifetime cumulative head‑impact force—including impacts before joining the NFL—is the strongest predictor of CTE.
“We can lower that cumulative impact without altering football itself,” he added, recommending that youth avoid tackle football and that all levels of the sport eliminate hitting during practice.
While the 25 % figure may startle casual observers, it is less surprising to those intimately familiar with the sport.
“I suspect the true number is even higher,” said Randy Grimes, 66, a former Tampa Bay Buccaneers center (1983‑1992). “Adding the untested cases would raise it further.”
At least two of his former offensive‑line teammates—guards Tom McHale (died at 45) and John Bruhin (died at 57)—were diagnosed with CTE, as was linebacker Keith McCants, who died at 53.
Applying the study’s rate to the rest of his teammates suggests he likely shared the field with dozens of players who either died undiagnosed or are living with undiagnosed CTE.
Grimes says he has not yet experienced symptoms that concern him about his cognition, but he runs a nonprofit that advises retired athletes—including football players—and has observed signs he believes may be linked to CTE.
“It’s rarely discussed, and players often avoid the topic,” Grimes said. “More open conversation could accelerate research, but many resist acknowledging the possibility. Deep down, many suspect that most of us will develop some form of CTE.”
Although hundreds of former NFL players have received a CTE diagnosis—usually after family members donate the brain due to troubling symptoms—the majority of cases remain private.
Only a handful become widely known, typically when linked to a prominent name such as Junior Seau, Ken Stabler, or Frank Gifford—all Pro Football Hall of Fame inductees.
Other cases gain notoriety when tied to criminal conduct that may partly stem from CTE, as with Aaron Hernandez and Phillip Adams, both of whom committed murder and were later found to have CTE.
In July 2025, Shane Tamura—a football player who never made an NFL roster—killed four individuals in a New York City building that houses the league’s headquarters; an autopsy later confirmed he had CTE.
CTE cannot be diagnosed while a person is alive, although some former players—such as Hall of Fame running back Tony Dorsett—believe they have it. Others, including Chris Borland and John Urschel, retired early to protect their brain health.
Despite the rising number of CTE cases, football’s popularity remains largely unaffected; the NFL reportedly generated over $23 billion in revenue in 2024.
“The NFL continually works to make football safer, including by adopting measures to cut concussions and head impacts,” the league stated. “It remains committed to providing the NFL community with a strong and growing array of resources to support physical and mental well‑being.”
The NFL Players Association said the study “serves as a sobering reminder that football entails genuine risks with lasting repercussions for players and their families.”
It added: “The findings should act as a call to action throughout the football world.”
Scientists anticipate being able to diagnose CTE in living individuals with high confidence, much like Parkinson’s and Alzheimer’s are currently identified.
At present, most former NFL players’ brains are never examined, leaving an undetermined number of potential CTE cases undiagnosed. Growing awareness has led more families to donate the brains of recently deceased players who showed CTE symptoms; these donations are not random, as clear signs of the disease are usually present.
In 2017, 110 out of the first 111 donated former NFL players’ brains were found to have CTE.
Unlike earlier work, this study applied CTE findings to the wider NFL population during the same period, rather than focusing solely on donated brains.
The researchers counted all former NFL players known to have died between 2008 and 2021—2,079 individuals—and discovered that 16.6 % (about one in six) had CTE.
They limited the analysis to the most recent six years, noting a rise in brain donations following several high‑profile CTE cases and the 2015 film Concussion (donations rose from 17 in 2014 to 53 in 2018 at what is now the UNITE Brain Bank).
Within that window, 235 brains were donated for study, and 215 of them showed at least some CTE pathology.
Under the most conservative assumptions, the researchers concluded that 24.5 % of the deceased players had CTE; this figure excludes brains examined by unaffiliated scientists (which cannot be verified) and cases strongly suspected of CTE based on symptoms but never confirmed post‑mortem.
Although most CTE diagnoses are not publicly disclosed, rough estimates can be informative. For example, thousands of former NFL players who suffered CTE may have played for the New York Giants; hundreds could have been coached by Bill Belichick or Pete Carroll; and at least several dozen may have been teammates of Tom Brady.
The expanding CTE case list yields striking insights: eight members of the 1972 Miami Dolphins—the only undefeated team in modern NFL history—have received a CTE diagnosis.
The most recent previously unreported case is Mercury Morris, the swift halfback who played eight NFL seasons, experienced headaches and drug addiction after retirement, and died in 2024 at age 77.
CTE is not limited to older retirees. The 2001 New England Patriots, Super Bowl champions, lost seven former players between ages 35 and 50, per the Boston Globe; at least three of those were confirmed to have CTE.
Applying the one‑in‑four ratio indicates that up to ten additional Patriots from that era could also have CTE.
The 2009 San Diego Chargers, who finished 13‑3, have three deceased players with publicly confirmed CTE diagnoses.
One is Vincent Jackson, a three‑time Pro Bowl receiver who died at 38 from alcohol poisoning in a hotel room. Another is Kevin Ellison, a defensive back who died at 31 after being struck by a car while wandering onto a California freeway.
The third is defensive back Paul Oliver, who was 29 in 2013 when he died by suicide on the stairs of his family home, witnessed by his wife Chelsea and their two young sons.
Paul Oliver’s widow, Chelsea, says she occasionally hears from his former teammates or their relatives, who worry they may be experiencing CTE effects. She believes the 25 % estimate understates the true prevalence.
“If we could test every living former player for CTE,” she said, “most would likely show the disease.”
She noted that her husband played four NFL seasons, endured multiple concussions, and subsequently changed—becoming someone “who just wasn’t himself.” He suffered headaches, grew delusional and paranoid, and increased his alcohol consumption. The couple discussed CTE shortly after longtime Chargers star Junior Seau, who ended his career with New England, shot himself in the chest to preserve his brain for analysis.
Discovering that, statistically, her husband may have had a dozen or more teammates with CTE—and that he was not alone—offers no comfort, Oliver said. “It just makes me sad.”
She does not expect fans to grasp the reality. When she reads comments on articles about former players behaving poorly or dying by suicide, she often sees remarks like, “They’re just blaming CTE.” She shakes her head, noting that such commentators lack firsthand experience, and she cannot blame them for their ignorance.
“To them,” she added, “concussions and CTE are somebody else’s problem.”
If you are having thoughts of suicide, call or text 988 to reach the 988 Suicide and Crisis Lifeline or go to SpeakingOfSuicide.com/resources for a list of additional resources.
