Prior research has demonstrated that cognitive inflexibility is associated with anxiety in autistic individuals. Everyday patterns of behavioral inflexibility (e.g. observable inflexible behavior in the context of the need to change or adapt and that is manifested in real-world everyday settings) is common in autism and can be distinguished from performance on discrete cognitive tasks that tap flexible attention, learning, or decision-making. The purpose of this study was to extend this prior work on inflexibility in autism but with measures specifically developed with input from stakeholders (caregivers and clinicians) for autistic youth designed to measure everyday behavioral inflexibility (BI). We characterized anxiety in a large sample of autistic (N = 145) and non-autistic youth (N = 91), ages 3 to 17 years, using the Parent Rated Anxiety Scale for Autism Spectrum Disorder (PRAS-ASD). Further, we sought to understand how BI, measured via the Behavioral Inflexibility Scale (BIS), predicted anxiety compared to other variables known to increase anxiety in youth (chronological age, IQ, autism diagnosis, assigned sex at birth). Autistic youth had higher parent-related anxiety and BI compared to non-autistic youth. BI was the strongest predictor of anxiety scores, irrespective of diagnosis. Overall, our findings highlight the importance of BI to the understanding of anxiety in autistic youth.