Objective: To examine the efficacy of a modular cognitive-behavioral therapy (CBT) protocol relative to treatment as usual (TAU) among children with high-functioning autism spectrum disorders (ASD) and clinically significant anxiety. Method: A total of 45 children (7-11 years of age) with high-functioning ASD and clinically significant anxiety were randomized to receive 16 sessions of weekly CBT or TAU for an equivalent duration. After screening, assessments were conducted at baseline, post-treatment, and 3-month follow-up. Raters were blind to treatment condition. Results: Youth receiving CBT showed substantial improvement relative to TAU on primary anxiety outcomes. Of 24 children randomized to the CBT arm, 18 (75%) were treatment responders, versus only 3 of 21 children (14%) in the TAU arm. Gains were generally maintained at 3-month follow-up for CBT responders. Conclusions: Relative to usual care, CBT adapted for anxious youth with high-functioning ASD demonstrates large effects in reducing anxiety symptoms. This study contributes to the growing literature supporting adapted CBT approaches for treating anxiety in youth with ASD. Clinical trial registration information--Cognitive-Behavioral Treatment for Anxiety Disorders in Children With Autism Spectrum Disorders; http://clinicaltrials.gov; NCT01178385. (Contains 1 figure and 3 tables.)