The psychometric properties of the Pediatric Anxiety Rating Scale (PARS), a clinician-administered measure for assessing severity of anxiety symptoms, were examined in 72 children and adolescents diagnosed with an autism spectrum disorder (ASD). The internal consistency of the PARS was 0.59, suggesting that the items were related but not repetitive. The PARS showed high 26-day test-retest (ICC = 0.83) and inter-rater reliability (ICC = 0.86). The PARS was strongly correlated with clinician-ratings of overall anxiety severity and parent-report anxiety measures, supporting convergent validity. Results for divergent validity were mixed. Although the PARS was not associated with the sum of the Social and Communication items on the Autism Diagnostic Observation System, it was moderately correlated with parent-reported inattention, aggression and externalizing behavior. Overall, these results suggest that the psychometric properties of the PARS are adequate for assessing anxiety symptoms in youth with ASD, although additional clarification of divergent validity is needed.