Objective: Anxiety following a traumatic brain injury (TBI) is a common problem; however, disparate prevalence estimates limit the clinical utility of research. The purpose of the current study was to examine how differences in methodological variables and sample characteristics impact on the prevalence of anxiety. Method: Data from 41 studies that examined either the prevalence of generalized anxiety disorder (GAD) diagnoses or clinically significant "cases" of self-reported anxiety following adult, nonpenetrating TBI were analyzed, and the impact of diagnostic criteria, measure, postinjury interval and injury severity was evaluated. Results: Overall, 11% of people were diagnosed with GAD and 37% reported clinically significant levels of anxiety following TBI. Prevalence estimates varied for different diagnostic criteria (range: 2%-19%), interview schedules (range: 2%-28%), and self-report measures (range: 36%-50%). GAD and "cases" of anxiety were most prevalent 2 to 5 years postinjury. The rates of GAD increased with injury severity (mild: 11%, severe 15%), but "cases" decreased (mild: 53%, severe: 38%), although neither difference was significant. Conclusions: Anxiety is common after a TBI and ongoing monitoring and treatment should be provided. Methodological and sample characteristics should be clear and well-defined, as differences across studies (e.g., how anxiety is conceptualized, which measure is used, time since injury, injury severity) impact prevalence rates.