The authors aim to determine if a history of traumatic brain injury (TBI) assessed before dementia onset is associated with a higher risk of neuropsychiatric symptoms after dementia onset. A population-based incident series of people with dementia were assessed for TBI prior to onset of dementia and for neuropsychiatric symptoms after the onset, using the Neuropsychiatric Inventory. Participants with predementia TBI were more likely to exhibit disinhibition (12.7% versus 5.4%, OR=2.8, p=0.02), but not other neuropsychiatric symptoms. Traumatic brain injury may increase the risk of disinhibition in patients with dementia.