Cognitive-behavioral therapy for anxiety in youth with an autism spectrum disorder appears efficacious; however, maintenance of treatment gains has not yet been studied. Using a sample of 32 youth who had benefited at least minimally from a past trial of cognitive-behavioral therapy for anxiety in autism spectrum disorder, this study assessed anxiety symptoms in youth 10--26 months following treatment completion. Compared to baseline, follow-up scores were associated with large effects for treatment. Relative to post-treatment, a small effect for return in symptoms was present and significantly fewer individuals were rated as responders at follow-up. Future studies should investigate factors associated with poor treatment maintenance and modifications or additions to treatment that may help maintain treatment gains.