Scientists and clinicians regularly use clinical screening tools for attention deficit/hyperactivity disorder (ADHD) to assess comorbidity without empirical evidence that these measures are valid in youth with autism spectrum disorder (ASD). We examined the prevalence of youth meeting ADHD criteria on the ADHD rating scale fourth edition (ADHD-RS-IV), the relationship of ADHD-RS-IV ratings with participant characteristics and behaviors, and its underlying factor structure in 386, 7–17 year olds with ASD without intellectual disability. Expected parent prevalence rates, relationships with age and externalizing behaviors were observed, but confirmatory factor analyses revealed unsatisfactory fits for one-, two-, three-factor models. Exploratory analyses revealed several items cross-loading on multiple factors. Implications of screening ADHD in youth with ASD using current diagnostic criteria are discussed.