DESCRIPTION (provided by applicant): Generalized anxiety disorder (GAD) is a chronic disorder that has been associated with significant psychosocial impairment, as well as health-care utilization/cost. Further, it is a highly comorbid disorder, and has been posited to be the basic anxiety disorder, which increases vulnerability for other anxiety and mood disorders. Despite the significant health impact of this disorder, it is currently the anxiety disorder for which existing treatments have demonstrated the least effectiveness. Cognitive-behavioral treatments have demonstrated the most efficacy to date; yet studies commonly find that less than half those treated meet criteria for high end state functioning after a follow-up period, indicating that more efficacious treatments are needed. In addition, very few studies have addressed the effect of treatment on quality of life and functioning or assessed gains over a long follow-up period. Current theory and research in the area of worry and GAD highlights the role of cognitive/experiential avoidance in this disorder, suggesting that an integrative treatment that combines elements of traditional cognitive-behavioral approaches with mindfulness/acceptance-based elements from other behavioral treatments may be beneficial with this population. Recent pilot work suggests that an acceptance-based behavior therapy specifically designed to target presenting problems in GAD results in significant reductions in symptomatology and increases in quality of life and that these changes are significantly greater than changes that occur over a waitlist period. The current application aims to further investigate the efficacy of this intervention by comparing it to Applied Relaxation, an intervention with demonstrated efficacy in treating GAD. We will randomly assign 126 individuals who meet criteria for GAD (as well as comorbid disorders, providing GAD is principal) to receive one of these two treatments. We will examine whether acceptance-based behavior therapy leads to significantly greater reductions in symptoms and increases in quality of life and functioning at post and across 24 months of follow up assessments. We will also determine the proportion of individuals who meet high end state functioning in each treatment, and we will explore whether treatment effects are comparable among ethnic minority individuals (who we will make considerable efforts to recruit) and non-minority individuals. Finally, we will explore whether treatment effects are due to proposed mechanisms of change (experiential acceptance, mindfulness) as well as potential predictors of response among either or both treatments. Findings will have important implications in terms of determining maximally efficacious interventions for GAD and guiding future research in this area.