Obsessive–compulsive disorder (OCD) is prevalent among youth with autism spectrum disorder (ASD). Cognitive–behavioral therapy (CBT) with ASD-specific modifications has support for treating OCD in this population; however, use of intensive CBT in youth with ASD and severe OCD has not been tested. The current study examined the preliminary effectiveness of an individualized intensive CBT protocol for OCD in adolescents with ASD. Nine adolescents (aged 11–17 years) completed a regimen of intensive CBT (range 24–80 daily sessions) incorporating exposure with response prevention (ERP). Treatment materials, language and techniques were modified in accordance with evidence-based findings for this population. Seven of nine participants (78%) were treatment responders, and large treatment effects (d = 1.35–2.58) were obtained on primary outcomes (e.g., obsessive–compulsive symptom severity). Preliminary findings suggest that an intensive CBT approach for OCD is effective among adolescents with ASD.