Lay summary – Traumatic brain injury may increase the risk of dementia later in life, but the reasons for this are not fully understood. This study looked at whether a history of TBI is linked to tiny areas of bleeding and small blood vessel changes in the brains of otherwise healthy midlife adults, including after mild injuries. The researchers also examined whether these brain changes relate differently to memory, movement, mood, sleep and vascular risk factors in people with and without TBI. The aim was to better understand whether some brain scan findings usually linked to small vessel disease may instead be caused by earlier head injury.