Aim & methods: Clinical characteristics were examined in 108 high-functioning youth (children with a full IQ scale of at least 70) with an autism spectrum disorder (ASD; aged 7–15 years) who were presenting for inclusion in one of four clinical trials examining the efficacy of cognitive behavioral therapy in youth with ASD and anxiety. Results: We present baseline characteristics of this cohort, including prevalence rates of anxiety and comorbid disorders, and correlates of anxiety (e.g., comorbid diagnoses, impairment, anxiety severity and mental health services received) as a function of age and ASD diagnosis in treatment-seeking youth. Primary anxiety disorders were: 41.7% (n = 45) social phobia, 25.9% (n = 28) generalized anxiety disorder, 15.7% (n = 17) separation anxiety disorder, 12.0% (n = 13) obsessive–compulsive disorder and 4.6% (n = 5) specific phobia. Overall, 91.6% of participants (n = 99) met criteria for two or more anxiety disorders. Parents reported considerable functional impairment as measured by the Columbia Impairment Scale and anxiety severity as measured by the Pediatric Anxiety Rating Scale; this did not statistically differ as a function of ASD diagnosis or age. Anxiety severity, the number of comorbid anxiety diagnoses and total comorbid diagnoses were directly associated with parent-reported child impairment. Youth with ASD and anxiety present as a heterogeneous cohort with significant impairments and complex diagnostic presentations. Conclusion: These data provide information about the nature of anxiety in youth with ASD, which may foster the development of tailored treatment protocols.