The goal of this study was to investigate the diagnostic and symptom specificity of a model of GAD that has four main features: intolerance of uncertainty, positive beliefs about worry, poor problem orientation, and cognitive avoidance. The authors compared 17 patients with non-comorbid generalized anxiety disorder (GAD) to 28 patients with non-comorbid panic disorder with agoraphobia (PDA) and found that only intolerance of uncertainty showed evidence of diagnostic specificity, i.e., intolerance of uncertainty scores were higher in the GAD group relative to the PDA group. In terms of symptom specificity, when both groups were combined, all model variables were significantly related to worry but unrelated to fear of bodily sensations, agoraphobic cognitions, and behavioral avoidance. Taken together, these findings provide further support for the link between intolerance of uncertainty and GAD and underscore the importance of pursuing the issue of specificity from both a diagnostic and symptom perspective.