Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social communication deficits and, similar to obsessive-compulsive disorder (OCD), restricted and repetitive behaviors. The restricted, repetitive patterns of behaviors and interests that are characteristic of ASD often resemble the obsessions and compulsions of OCD, which can make it difficult to distinguish or differentiate the two conditions. A common challenge in diagnosing comorbid ASD and OCD is the apparent overlap in symptoms between the two disorders. This chapter discusses the differentiation between OCD and ASD, the assessment and diagnosis of OCD within the context of ASD, and the treatment of this presentation of OCD.