Anxiety often co-occurs with autism spectrum disorder, yet there are few valid and reliable instruments for measuring anxiety in youth with autism spectrum disorder. This article describes the modification of the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder and systematic psychometric evaluation in a well-characterized sample of 116 youth (age: 5-17 years) with autism spectrum disorder and a range of anxiety symptoms. The clinician-administered-Pediatric Anxiety Rating Scale for youth with autism spectrum disorder was modified with input from parents of children with autism spectrum disorder and an expert panel. Unlike many other anxiety measures, the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder is more focused on behavioral manifestations of anxiety versus verbal expression. Results provide preliminary support for the psychometric properties of the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder. The internal consistency of the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder was 0.90. The Pediatric Anxiety Rating Scale for youth with autism spectrum disorder was strongly correlated with parent-report anxiety measures (rs=0.62-0.68), supporting convergent validity. In support of divergent validity, correlations between the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder and parent ratings of autism spectrum disorder symptoms, social withdrawal, stereotypy, hyperactivity, inappropriate speech, and repetitive behaviors were low (rs=0.13-0.32). The Pediatric Anxiety Rating Scale for youth with autism spectrum disorder was moderately correlated with parent-reported irritability (r=0.52). The Pediatric Anxiety Rating Scale for youth with autism spectrum disorder showed good test-retest reliability (intraclass correlation coefficient=0.75-0.82) and inter-rater reliability (ICCs=0.70-0.92). Overall, results support the use of the Pediatric Anxiety Rating Scale for youth with autism spectrum disorder for assessing anxiety in youth with autism spectrum disorder.