The best-known count is 345 former NFL players whose donated brains were found to have chronic traumatic encephalopathy (CTE) in a Boston University research program. That number describes a selected group of brain donors, not all football players.
There is no complete count of every player who has had CTE, and the condition is currently confirmed by examining brain tissue after death. Here’s what the reported figures do—and don’t—tell you, how researchers identify CTE, and what is known about football-related risk, symptoms, and prevention.
how many football players have had cte? The best-known count
The figure most often cited is 345 former NFL players. Boston University’s CTE Center reported that its researchers had diagnosed CTE in 345 of 376 former NFL players whose brains had been donated for research. The reported share is about 92% of that donor group.
That is a striking finding, but it does not mean 92% of all NFL players have CTE. The brains came from people whose families chose to donate them, often because the player had experienced concerning symptoms or a suspected history of brain injury. This makes the group very different from a randomly selected sample of all players.
There is no reliable total for every football player ever diagnosed, at any level. A confirmed diagnosis currently requires examining brain tissue after death, and no national system counts every case among former professionals, college athletes, high school players, and youth players.
Why different reports give different numbers
The count changes as families donate more brains and researchers examine them. News reports may also refer to different dates, study groups, or levels of play. A figure from one research program should not be mistaken for a count of all diagnosed players.
Another widely reported study, published in 2017 in the medical journal JAMA, found CTE in 110 of 111 former NFL players’ brains examined. It also found CTE in 48 of 53 former college players’ brains in its sample. Those figures describe that study’s donated brains, not the overall populations of NFL or college players.
The 2017 study and the Boston University tally are often discussed together, but they are not interchangeable population surveys. They cover selected donors and may differ in the dates and group of brains examined. The key point is consistent: CTE has been found in former players at multiple levels, while these donor studies cannot establish how common it is among all players.
What the reported percentages can—and cannot—tell you
A percentage based on donated brains answers a narrow question: how many brains in that particular collection showed the characteristic changes researchers were looking for? It does not answer how many players in the wider population have the disease.
This is a form of selection bias. Families may be more likely to donate a brain when a player had memory problems, mood changes, or a suspected history of repeated head impacts. If people with concerns are overrepresented, the share with CTE in a donor group can be much higher than the share among all former players.
There is a second limitation: the overall number of players who might be affected is unknown. Researchers cannot calculate a population rate from a group of donors unless they know how likely every player was to be included and why. The donor figures do not supply that information.
So, the careful answer is not “most football players have CTE.” It is that researchers have confirmed CTE in hundreds of donated brains, including many former football players, but do not yet know the condition’s prevalence among all players.
| Figure or finding | What it describes | Best way to interpret it |
|---|---|---|
| 345 of 376 former NFL players | Brains in a Boston University research collection | A donor-group finding, not an NFL-wide rate |
| 110 of 111 former NFL players | Brains in a 2017 published study | A separate, highly selected group of donors |
| 48 of 53 former college players | Brains in the college-player group in that study | Evidence CTE has occurred in former college players, not a college-wide estimate |
| No complete total for all football players | Cases across all ages and levels of play | There is no population-wide count or living diagnostic test |
What CTE is and how researchers diagnose it
Chronic traumatic encephalopathy, or CTE, is a degenerative brain disease associated with repeated head impacts. Those impacts can include concussions and impacts that do not cause obvious concussion symptoms. The disease is identified by a distinctive pattern of abnormal tau protein in brain tissue.
Tau is a protein that normally helps support brain cells. In CTE, abnormal tau builds up in a particular pattern, including around small blood vessels and in parts of the brain. Researchers look for that pattern under a microscope after death.
CTE cannot currently be definitively diagnosed in a living person. A clinician can assess symptoms, medical history, and other possible conditions, but those steps cannot confirm the characteristic brain-tissue changes. A person may have concerning symptoms without having CTE, and someone with CTE changes in the brain may not have had clear symptoms during life.
That distinction matters because memory problems, depression, irritability, sleep trouble, and difficulty concentrating can have many causes. These can include other neurological conditions, mental health issues, substance use, medication effects, or ordinary medical problems. Symptoms alone are not proof of CTE.
Does playing football cause CTE?
Research supports an association between repeated head impacts and CTE. Football involves frequent collisions, and some players experience repeated impacts over many seasons. However, the existence of CTE in a donated brain does not establish exactly when or how the disease developed in that individual.
Researchers continue to study how risk may relate to the number, intensity, and duration of head impacts. Risk is not necessarily the same for every player. A history of concussions is important, but concussion count alone does not capture all head impacts, and it cannot predict with certainty whether a person will develop CTE.
It is also important not to overstate what the evidence says. A confirmed case shows that CTE occurred in that person. It does not prove that every person who plays football will develop CTE, nor does it establish a precise risk percentage for a particular player or position.
Football is not the only activity associated with repeated head impacts. CTE has also been reported in people who participated in other contact sports and activities. Those findings do not make the risks identical across sports; they show that the research question concerns repeated impacts, not one sport alone.
What symptoms have been reported in people with CTE?
Researchers and families have described changes in thinking, mood, behavior, and daily functioning among some people whose brains were later found to have CTE. Reported concerns include memory difficulties, impaired attention, impulsive behavior, depression, irritability, and problems with planning or judgment.
These reports do not create a symptom checklist that can diagnose the disease. The same problems can occur for many reasons, and researchers are still working to understand how brain changes relate to symptoms over a person’s lifetime. CTE findings after death do not mean every symptom that occurred beforehand was caused by CTE.
Reports of suicidal thoughts or behavior in a person with CTE also need careful interpretation. A diagnosis found after death cannot, by itself, prove what caused an individual’s distress or actions. Mental health and safety concerns deserve immediate attention regardless of whether CTE is suspected.
How CTE compares with concussion and other brain conditions
A concussion is a brain injury that can happen after a blow or jolt to the head or body. It is assessed based on symptoms and clinical evaluation. CTE, by contrast, is a brain disease identified by a specific pattern of changes in tissue after death. They are related areas of concern, but they are not the same diagnosis.
Having a concussion does not mean a person has CTE. Likewise, a person can experience repeated head impacts without recognizing or reporting a concussion every time. This is one reason researchers examine exposure to impacts as well as diagnosed injuries.
Other conditions can also affect memory, mood, and thinking. Doctors may evaluate sleep, mental health, medications, alcohol or drug use, neurological disease, and other health factors. A thorough assessment can help identify treatable causes and support a person’s needs, even though it cannot confirm CTE during life.
What players, families, and coaches can do now
There is no proven way to guarantee that a player will avoid CTE, and no treatment can currently reverse confirmed CTE brain changes. Still, practical choices can reduce avoidable head impacts and make it more likely that injuries receive appropriate attention.
- Report symptoms promptly. A player with headache, dizziness, confusion, nausea, vision problems, or other symptoms after a hit should stop playing and be assessed by a qualified health professional. Returning before recovery can expose the player to further injury.
- Follow a gradual return-to-play process. After a suspected concussion, the player should not return to contact practice or competition until cleared under the applicable medical and sports rules. A rushed return can make recovery harder and put the player at additional risk.
- Reduce unnecessary contact. Coaches and teams can limit full-contact drills, teach safer tackling and blocking techniques, and enforce rules against dangerous hits. Fewer avoidable impacts mean less exposure, even though no single measure can remove all risk.
- Use properly fitted, maintained equipment. A helmet can help protect against some injuries, but it does not prevent every concussion or stop all forces from reaching the brain. Do not treat helmet use as a guarantee of protection.
- Take ongoing health concerns seriously. Persistent changes in memory, mood, sleep, or behavior deserve evaluation. A clinician can look for causes and care options without claiming to diagnose CTE.
A useful point that often gets missed is that “no diagnosed concussion” does not mean “no head impacts.” Players and families should consider the full history of contact exposure, not only the number of injuries officially labeled concussions. That history can help a clinician understand the context, although it still cannot establish a CTE diagnosis.
Common questions about football and CTE
Does 345 out of 376 mean 92% of NFL players have CTE?
No. It means researchers found CTE in about 92% of the former NFL players whose brains were included in that donor group. Because the brains were donated and the group was not randomly selected, the percentage cannot be applied to all NFL players.
How many high school or youth football players have had CTE?
There is no complete count or reliable population rate for high school or youth players. CTE has been identified in some donated brains from people who played football at different levels, but a small number of cases cannot show how common it is among all young players.
Can a brain scan or blood test tell someone they have CTE?
No currently accepted scan or blood test can definitively diagnose CTE in a living person. Tests may help doctors assess symptoms or rule out other conditions, but confirmation of CTE requires examination of brain tissue after death.
Can someone have CTE without having had a diagnosed concussion?
Yes. A diagnosed concussion is not the only kind of head impact that may matter, and some impacts do not produce symptoms that are recognized or reported as concussion. Researchers are still studying how different patterns of exposure relate to CTE risk.
Does everyone with CTE develop the same symptoms?
No. Symptoms and their timing can differ, and some symptoms commonly linked to CTE can have other causes. The presence of a specific symptom does not confirm CTE, and brain changes do not necessarily predict one person’s experience during life.
The clearest widely cited count is 345 former NFL players in a research brain-donor group, not 345 out of every 376 players in the league. These findings show that CTE has been confirmed in many former players, but they cannot establish how common it is among all football players.
If you or someone you care about has ongoing symptoms after playing, arrange a medical evaluation and share the full history of head impacts. For prevention, focus on reporting injuries, limiting unnecessary contact, and following a careful return-to-play process; no helmet or symptom checklist can rule CTE in or out.