Background: The use of maladaptive behaviors by individuals with generalized anxiety disorder (GAD) is theoretically important and clinically meaningful. However, little is known about the specificity of avoidant behaviors to GAD and how these behaviors can be reliably assessed. Aims: This study replicated and extended the psychometric evaluation of the Worry Behaviors Inventory (WBI), a brief self-report measure of avoidant behaviors associated with GAD. Method: The WBI was administered to a hospital-based sample of adults seeking treatment for symptoms of anxiety and/or depression (n = 639) and to a community sample (n = 55). Participants completed measures of symptom severity (GAD, depression, panic disorder, health anxiety, and personality disorder), and measures of checking, reassurance-seeking and behavioral inhibition. Analyses evaluated the factor structure, convergent, divergent, incremental, and discriminant validity, as well the temporal stability and treatment sensitivity of the WBI. Results: The two-factor structure found in the preliminary psychometric evaluation of the WBI was replicated. The WBI was sensitive to changes across treatment and correlated well with measures of GAD symptom severity and maladaptive behaviors. The WBI was more strongly related to GAD symptom severity than other disorders. The WBI discriminated between clinical and community samples. Conclusions: The WBI provides clinicians and researchers with a brief, clinically meaningful index of problematic behaviors that may guide treatment decisions and contribute to our understanding of maintaining factors in GAD.