This study examined optimal guidelines to assess treatment response and remission for anxiety in youth with autism spectrum disorders (ASD) using the Pediatric Anxiety Rating Scale (PARS). Data was collected for 108 children aged 7-16 years with comorbid anxiety and ASD before and after receiving cognitive behavior therapy. Optimal cut-offs on the PARS were assessed using signal detection analyses using receiver operating characteristic methods. Maximum agreement with response criteria was achieved at 15% reduction in symptoms on the PARS. Maximum agreement with remission criteria was achieved at 40% reduction in symptoms, or at a score of 10 or below at post-treatment. Results have implications for standardizing criteria used in research trials and clinical practice.