The frequent co-occurrence of anxiety disorders and autism spectrum disorders (ASD) in youth has spurred study of intervention practices for this population. As anxiety disorders in the absence of ASD are effectively treated using cognitive-behavioral therapy (CBT) protocols, an initial step in evaluating treatments for comorbid youth has necessarily centered on adaptation of CBT. One primary limitation of this research, to date, is that interventions for adolescents with anxiety disorders and ASD have not been systematically tested. In this study, 20 adolescents (90% male) with ASD and a comorbid anxiety disorder, between ages 11 and 14 years (M = 12.2 years, SD = 1.11 years), participated in an open trial of modified CBT targeting anxiety with ASD. Findings demonstrated significant reductions in anxiety severity, as assessed by clinician and parent ratings, from baseline to post-treatment. In addition, reductions in parent-rated externalizing symptoms were observed. Gains were maintained at a 1-month follow-up.