Anxiety disorders are commonly diagnosed in children with autism, Asperger syndrome (AS), and pervasive developmental disorder not otherwise specified (PDD-NOS). Anxiety disorders contribute to children's functional impairment over and above the functional deficits attributable to autism, AS, and PDD-NOS. Thus, investigators have called for the development of anxiety treatments for this population (Attwood, 2003). Cognitive behavioral therapy (CBT) has been found to be efficacious for anxiety disorders in typically developing children. This pilot study will advance the field by providing an estimate of the treatment effects of CBT for anxiety disorders among children with autism, AS, or PDD-NOS. The sample will include 20 children aged 7-11 years with autism, AS, or PDD-NOS and a comorbid anxiety disorder. Children will be randomly assigned to immediate treatment or a 3-month waitlist. The manualized CBT program includes traditional anxiety treatment components including coping skills training (e.g., cognitive restructuring), in vivo exposure, operant procedures, and parent training. Additional treatment components have been added to enhance intervention response in children with AS or PDD-NOS, including emotion education, social skills/friendship skills training, and peer tutoring/mentoring modules. Trained graduate students with expertise in CBT and developmental disabilities will serve as therapists. Treatment fidelity will be checked using a session-by-session adherence checklist. Treatment acceptability and consumer satisfaction will be assessed at posttreatment, providing guidance on the extent to which the manual will need to be revised. Multiple measures of children's anxiety, including a structured diagnostic interview administered by an independent evaluator, will comprise the primary outcomes. Children's social functioning, adaptive behavior, and service use will also be assessed to determine if CBT can affect relevant distal outcomes. By comparing outcomes for children in the immediate treatment group versus those in the waitlist group, we will estimate effect sizes of CBT for this population. Subsequently, power analyses will be conducted in planning for a larger clinical trial. This study could contribute to public health efforts to address the mental health needs of the rising number of children diagnosed with autism-spectrum disorders. If CBT is found to be efficacious, it will be the first evidence-based psychological treatment to be successfully adapted for children with autism, AS, and PDD-NOS.