Anger outbursts (AO) are associated with severe symptoms, impairment and poorer treatment outcomes for anxious children, though limited research has examined AO in youth with co-occurring autism and anxiety disorders. This study examined AO in children with autism and anxiety by evaluating clinical characteristics, family accommodation, and changes in AO following anxiety-focused treatment. The sample comprised 167 youth with autism and anxiety enrolled in a multi-site randomized clinical trial comparing standard care CBT for anxiety, CBT adapted for youth with autism, and usual care. Most participants (60%) had AO, which contributed to impairment above and beyond anxiety and autism. AO impacted functional impairment indirectly through a pathway of parental accommodation. AO reduced with anxiety-focused treatment. Findings highlight that AO are common in this population and uniquely contribute to functional impairment, indicating a need for direct targeting in treatment.