Obsessive-compulsive and related disorders (OCRDs) are a group of diagnoses that center on compulsive behaviors and/or obsessive thoughts. They include obsessive-compulsive disorder (OCD), body dysmorphic disorder (BDD), hoarding disorder, excoriation disorder, and trichotillomania. Each of the OCRDs are associated with significant psychosocial impairment and family/caregiver burden. Furthermore, these disorders frequently co-occur with autism spectrum disorder (ASD) traits and diagnoses, and differential diagnosis can be difficult. OCD represents the most common of the OCRDs, and also the most well researched to date. Consequently, this chapter focuses on the nature and impact of comorbid OCD and ASD across the lifespan. Unfortunately, preliminary research indicates that individuals with OCD and ASD are significantly more disadvantaged by way of poorer psychosocial functioning, increased family burden/accommodation to symptoms, greater number of other comorbid conditions, and more likely to present with comorbid externalizing disorders. Future research is needed to determine what impact these unique complexities may have on treatment success. Preliminary research suggests that cognitive behavioral therapy (CBT) is of benefit to these individuals with comorbid ASD and OCD; however, modification may be necessary to improve engagement and outcomes (e.g., family inclusion in therapy). This chapter presents a case example of modified CBT for a child with comorbid ASD and OCD, delivered intensively. Future research should focus on the related OCRDs in individuals with ASD, as well as improving current assessment and treatment practices.