Anxiety may exacerbate interpersonal difficulties and contribute to secondary behavioral problems in adolescents with High-Functioning Autism Spectrum Disorder (HFASD). This study was conducted to assess the psychometric properties and construct validity of measures of anxiety with a sample (n = 30) of adolescents with HFASD and comorbid anxiety disorders. Results indicate that the measures (CASI-Anxiety Scale; Sukhodolsky et al. 2008; MASC; March 1998) possess acceptable internal consistency, and there is evidence of discriminant validity. Most of the adolescents, however, under-reported problems with anxiety, compared to parent-reported and clinician-derived reports and given they were seeking treatment for anxiety problems. Findings highlight the importance of using multiple raters in clinical practice and consideration of rater discrepancies in clinical research.