Purpose/Objective: The goals of the present study were (1) to document the prevalence of anxiety-related disorders and anxiety symptoms at 4, 8, and 12 months post-injury in individuals with mild traumatic brain injury (mTBI) while considering pre-injury history of anxiety disorders and (2) to verify whether the presence of anxiety in the first months following mTBI was associated with more symptoms present one year after the injury. Research Method/Design: One hundred and twenty participants hospitalized after an accident and having sustained mTBI were assessed at 4, 8, and 12 months post-accident with the Mini-International Neuropsychiatric Interview, the Hospital Anxiety and Depression Scale and questionnaires assessing fatigue, irritability, perceived stress, cognitive difficulties, depression, insomnia, and pain. Results: At 4 months, 23.8% of participants presented with at least one anxiety-related disorder compared to 15.2% at 8 months and 11.2% at 12 months. Overall, 32.5% presented with at least one anxiety disorder over the first 12 months post-mTBI. Participants with a history of anxiety (20.5%) were significantly more anxious following their accident. Individuals who were anxious 4 months after the accident presented with more symptoms in different areas 12 months post-injury compared to non-anxious individuals. Conclusions/Implications: The present results highlight that anxiety should be evaluated and managed carefully as it appears to be a key factor in the persistence of other mTBI-related symptoms.