It is now well established that adults who present to speech clinics for help with stuttering will have an increased risk of having an anxiety disorder, particularly social anxiety disorder. Concomitant psychological problems are known to interfere with the maintenance of the benefits of behavioral speech treatments for stuttering. The current team has developed and trialed a cognitive behavior therapy (CBT) program designed specifically to reduce anxiety in adults who stutter, and trials have shown promise for both an in-clinic version and a standalone internet-based version. The aim of the present study is to determine whether iGlebe, the internet-based version of the team's internet CBT treatment (previously known as CBTPsych), enhances the benefits of behavioral stuttering treatment. Participants were 32 adults seeking treatment for stuttering. The design was a two-arm randomized experimental trial with blinded outcome assessments at 6 and 12 months post-randomization. Both arms received basic speech-restructuring training to reduce stuttering, without any anxiolytic (anxiety reducing) components. The experimental arm also received 5 months access to iGlebe. There was evidence that, at 12 months post-randomization, iGlebe added clinically significant improvements to self-reported stuttering severity and quality of life. The present experimental trial provides the first evidence that the addition of CBT to speech restructuring improves speech outcomes. The present results will be the basis for the development of a comprehensive, internet-based treatment program for anxiety associated with stuttering. Ultimately, it may be possible for such an economical, scalable, and translatable comprehensive treatment model to supplement standard speech-language pathology treatment practices for those who stutter.