Recent research has sought to identify maladaptive behaviors that are associated with generalized anxiety disorder (GAD). Although maladaptive behaviors may contribute to the maintenance of the disorder, little is known about how these behaviors change during the course of cognitive behavior therapy and whether such changes relate to treatment outcomes. This study examined changes in maladaptive behaviors, symptoms of GAD and depression, and disability across internet-based cognitive behavior therapy (iCBT) for GAD in two large clinical samples (N = 206 and 298). Assessments were completed at pre and post-treatment. Significant reductions in patients' maladaptive behaviors (WBI), GAD and depression severity (GAD-7 and PHQ-9), and disability (WHODAS-II) were observed following iCBT. Reductions in maladaptive behaviors predicted post-treatment GAD symptom severity after controlling for pre-treatment GAD symptom severity and reductions in depression and disability. Findings provide further support for the importance of maladaptive behaviors in contemporary conceptualizations of GAD and highlight the need for experimental investigations to examine the possible causal relationships between maladaptive behaviors and GAD.