Object Mild traumatic brain injury (TBI) has been proposed as a risk factor for development of Alzheimer’s disease, Parkinson’s disease, depression, and other illnesses. This study’s objective was to determine the association of prior mild TBI with subsequent diagnosis (i.e., at least one year post-injury) of neurologic or psychiatric disease. Methods All studies from 1995–2012 reporting TBI as a risk factor for diagnoses of interest were identified by searching PubMed, study references, and review articles. Reviewers abstracted the data and assessed study design and characteristics. Results 57 studies met inclusion criteria. A random effects meta-analysis revealed a significant association of prior TBI with subsequent neurologic and psychiatric diagnosis. The pooled odds ratio (OR) for TBI on development of any illness was 1.67 (95% CI 1.44–1.93, p<.001). Prior TBI was independently associated with both neurologic [OR 1.55 (95% CI 1.31–1.83, p<.001)] and psychiatric [OR 2.00 (95% CI 1.50–2.66, p<.001)] outcomes. Analyses of individual diagnoses found higher odds of Alzheimer’s disease, Parkinson’s disease, mild cognitive impairment, depression, mixed affective disorders, and bipolar disorder in individuals with previous TBI compared to those without TBI. This association was present when examining only studies of mild TBI and when considering the influence of study design and characteristics. Analysis of a subset of studies found no evidence that multiple TBIs were associated with higher odds of disease than a single TBI. Conclusions History of TBI, including mild TBI, is associated with the development of neurologic and psychiatric illness. This indicates that either TBI is a risk factor for heterogeneous pathologic processes or that TBI may contribute to a common pathologic mechanism.

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