Comorbid anxiety is common among children with Autism Spectrum Disorder (ASD), and parents of children with ASD are more likely to have anxiety disorders. This study investigated the relationship between parents' state and trait anxiety and parent-reported internalizing and externalizing symptoms among adolescents (n = 30) with ASD, as well as the relationship of parents' anxiety symptoms and adolescent treatment response in the context of a randomized controlled trial. Parental state anxiety correlated with severity of adolescent anxiety, and trait anxiety in parents correlated with parent-reported adolescent internalizing and externalizing symptoms. Also, parents of adolescent treatment responders experienced a decrease in their own trait anxiety. Findings highlight the importance of considering parental anxiety when targeting anxiety among youth with ASD.