Objectives: Traumatic brain injury (TBI) is common in military personnel, and there is growing concern about the long-term effects of TBI on the brain; however, few studies have examined the association between TBI and risk of dementia in veterans.Methods: We performed a retrospective cohort study of 188,764 US veterans aged 55 years or older who had at least one inpatient or outpatient visit during both the baseline (2000)(2001)(2002)(2003) and follow-up (2003-2012) periods and did not have a dementia diagnosis at baseline. TBI and dementia diagnoses were determined using ICD-9 codes in electronic medical records. Fine-Gray proportional hazards models were used to determine whether TBI was associated with greater risk of incident dementia, accounting for the competing risk of death and adjusting for demographics, medical comorbidities, and psychiatric disorders.Results: Veterans were a mean age of 68 years at baseline. During the 9-year follow-up period, 16% of those with TBI developed dementia compared with 10% of those without TBI (adjusted hazard ratio, 1.57; 95% confidence interval: 1.35-1.83). There was evidence of an additive association between TBI and other conditions on risk of dementia.Conclusions: TBI in older veterans was associated with a 60% increase in the risk of developing dementia over 9 years after accounting for competing risks and potential confounders. Our results suggest that TBI in older veterans may predispose toward development of symptomatic dementia and raise concern about the potential long-term consequences of TBI in younger veterans and civilians. There is growing evidence that traumatic brain injury (TBI) is associated with a variety of shortand long-term adverse health outcomes. A 2008 Institute of Medicine report concluded that TBIs are consistently associated with an increased risk of unprovoked seizures, premature mortality, and neurocognitive deficits in the affected region, with evidence strongest for penetrating wounds and severe or moderate TBIs.1 However, prior research on the relationship between TBI and risk of Alzheimer disease (AD) and all-cause dementia has been mixed. [2][3][4][5][6][7][8][9][10][11][12][13][14] Most prior studies have not adequately controlled for potential confounders, such as medical and psychiatric comorbidities, and none have considered death as a competing risk.Furthermore, to our knowledge, only one prior study has specifically focused on examining the relationship between TBI and risk of dementia in veterans.11 Many veterans have other combatrelated risk factors such as posttraumatic stress disorder (PTSD) and depression, which have been associated with an increased risk of dementia in veterans in prior studies, 15,16 and could act as either confounders or effect modifiers of the association between TBI and dementia in veterans.