Obsessive-compulsive disorder (OCD) is a treatable condition that often requires specialist care, particularly when comorbid with autism spectrum disorder (ASD). However, specialist clinics are few and typically located in large medical centers. To increase availability of evidence-based treatment for OCD in individuals with ASD, we adapted an internet-delivered cognitive behavior therapy (ICBT) protocol to suit the needs of these individuals and conducted a feasibility study (N = 22). The primary outcome was the clinician-rated Children's Yale-Brown Obsessive-Compulsive Scale (CY-BOCS), administered at pre- and post-treatment as well as 3 months after treatment. ICBT was deemed acceptable and was associated with clinically significant improvements in CY-BOCS scores, corresponding to a large within-group effect size (Cohen's d = 1.33). Similarly, significant improvements were observed in most of the secondary parent- and self-rated measures. Approximately 60% of the participants were classed as treatment responders and 50% were in remission from their OCD at the 3-month follow-up. To provide a meaningful benchmark, we also analyzed data from a specialist clinic that regularly treats individuals with comorbid OCD and ASD (N = 52). These analyses indicated that specialized in-person CBT produced significantly larger effects (d = 2.69) while being markedly more resource demanding, compared to ICBT. To conclude, ICBT can be successfully adapted to treat OCD in youth with ASD and may be a viable alternative for those who do not have direct access to highly specialized treatment. Further improvements of the treatment protocol based on participant and therapist feedback are warranted, as is a formal test of its efficacy and cost-effectiveness in a randomized controlled trial.