Objective Attention bias modification treatment (ABMT) is a promising novel treatment for anxiety disorders, but clinical trials have focused largely on stand-alone formats among adults. This randomized controlled trial examined the augmenting effects of threat-based ABMT on cognitive behavioral therapy (CBT) in clinically anxious youth. Method Sixty-three treatment-seeking children with anxiety disorder were randomly assigned to 1 of the following 3 treatment groups: ABMT + CBT; ABMT placebo + CBT; and CBT-alone. Participants in the 2 ABMT conditions received repeated training on dot–probe tasks either designed to shift attention away from threats (active) or designed to induce no changes in attention patterns (placebo). Primary outcome measures were frequency and severity of anxiety symptoms as determined by a clinician using a semi-structured interview. Self- and parent-rated anxiety measures and threat-related attention bias scores were also measured before and after treatment. Results Both the active and placebo ABMT groups showed greater reductions in clinician-rated anxiety symptoms than the CBT-alone group. Furthermore, only the active ABMT group showed significant reduction in self- or parentrated anxiety symptoms. Finally, all groups showed a shift in attention patterns across the study, starting with a bias toward threat at baseline and shifting attention away from threat after treatment. Conclusions Active and placebo ABMT might augment the clinical response to CBT for anxiety. This effect could arise from benefits associated with performing computer-based paradigms such as the dot–probe task. Given the absence of group differences in attention-bias changes during treatment, possible mechanisms and methodological issues underlying the observed findings are discussed. Clinical trial registration information—Augmenting Effects of ABMT on CBT in Anxious Children: A Randomized Clinical Trial; http://clinicaltrials.gov/; NCT01730625.