Recent advances in the understanding of worry have led to the development of treatments for generalized anxiety disorder (GAD). The present study tested a GAD treatment that targeted intolerance of uncertainty, erroneous beliefs about worry, poor problem orientation, and cognitive avoidance. Twenty-six primary GAD patients were randomly allocated to a treatment condition (n = 14) or a delayed treatment control condition (n = 12). Self-report, clinician, and significant other ratings assessed GAD and associated symptoms. The results show that the treatment led to statistically and clinically significant change at posttest and that gains were maintained at 6- and 12-month follow-ups. Furthermore, 20 of 26 participants (77%) no longer met GAD diagnostic criteria following treatment. With regard to the treatment's underlying model, the results show that intolerance of uncertainty significantly decreased over treatment and that gains were maintained at both follow-ups. Although nonspecific factors were not significant predictors of treatment outcome, their role in the treatment of GAD requires further investigation.