Objective To determine at 1 year after moderate to severe traumatic brain injury the (1) rate of clinically significant anxiety; (2) rates of specific symptoms of anxiety; (3) risk factors for anxiety; and (4) associations of anxiety with other 1-year outcomes, including participation and quality of life. Design Prospective longitudinal observational study. Setting Inpatient rehabilitation centers, with data capture at injury and 1-year follow-up. Participants Persons with moderate to severe traumatic brain injury who were enrolled in the Traumatic Brain Injury Model Systems database (N=1838). Interventions Not applicable. Main Outcome Measures The 7-item Generalized Anxiety Disorder Scale, Patient Health Questionnaire (9-item screen for depression), FIM, Participation Assessment with Recombined Tools-Objective, and Satisfaction with Life Scale. Results Clinically significant anxiety was reported by 21% of the participants. Of these, >80% reported interference with daily activities, with the most common symptoms being excessive worry and irritability. A common pattern was comorbid anxiety and depression, with smaller proportions reporting either disorder alone. Anxiety had large effect sizes with respect to life satisfaction and cognitive disability and medium to small effect sizes relative to societal participation and self-care. Middle age, black race, lower socioeconomic status, preinjury mental health treatment, and at least 1 traumatic brain injury prior to the index injury were all risk factors for later anxiety. Conclusions Anxiety should be screened, fully evaluated, and treated after moderate to severe traumatic brain injury. Worry and irritability might be treated with pharmacologic agents or relatively simple behavioral interventions, which should be further researched in this population.