The current study examined the impact of comorbidity on cognitive and behavioral therapies for generalized anxiety disorder (GAD) as well as the impact of these therapies on diagnoses comorbid to GAD. Seventy-six treatment-seeking adults with principal diagnoses of GAD received 14 sessions of therapy. Most (n=46; 60.5%) of the sample had at least one comorbid diagnosis. Although the presence of comorbid diagnoses was associated with greater severity of GAD symptoms at pretreatment, greater severity of comorbid major depression, simple phobia, and social phobia was associated with greater change in symptoms of GAD in response to treatment, with no effect on maintenance of gains during a 2-year follow-up. Further, psychotherapy for principal GAD led to a reduction in number of comorbid diagnoses and in severity of social phobia, simple phobia, and major depression at posttreatment. At 2-year follow-up severity of social and simple phobia remained below pretreatment levels, whereas severity of depression was no longer significantly below pretreatment levels. These results suggest that although people with comorbid disorders enter treatment with more severe GAD symptomatology, they demonstrate greater change, and therefore such comorbidity does not diminish the efficacy of cognitive and behavioral therapies for GAD. In addition, the impact of these treatments for GAD may generalize to reduced severity of simple phobia, social phobia, and major depression; however, gains in severity of major depression are not maintained.