Current research suggests obsessive-compulsive disorder (OCD) co-occurs in around 20% of people with hoarding disorder (HD). The article discusses the theoretical conceptualization of co-occurring HD and OCD (HD+OCD), highlighting similarities between the disorders that may contribute to comorbidity, such as potentially overlapping etiological factors, comorbidity profiles, and phenomenological aspects; and differences that are important to consider in differential diagnosis and conceptualization, such as belief patterns, ego-syntonicty/dystonicity, and trajectory. The combination of HD+OCD versus either disorder alone appears to be associated with a profile characterized by higher nonhoarding OCD symptoms, anxiety symptoms, depression, and tic disorders, and which may be more treatment-refractory. The authors discuss some commonly used measures to assess hoarding that may be relevant in the context of OCD, as differential diagnosis of hoarding behaviors is often difficult, and hoarding may be difficult to detect in patients with OCD, especially in children. The article ends with a discussion on considerations for the treatment of HD+OCD with cognitive-behavioral therapy, as hoarding symptoms are less likely to respond to gold-standard exposure and response prevention, and there are no established treatment protocols that are designed to treat co-occurring HD and OCD.