Background: There is limited knowledge about obsessive-compulsive disorder (OCD) in people with intellectual disabilities (IDs). This paper describes the manifestation of compulsive behaviors associated with OCD at the behavioral level in people with ID in institutionalized settings. The aim was to gain nuanced insight into appropriate understanding and classification in this specific context, and derive implications for research and practice. Methods: Individual cases of people with ID (n = 7) were studied to assess compulsive symptoms through two days of on-site observation of the person with ID within the institution, guided group discussions (n = 28), and semi-structured interviews with key informants and caregivers of the person with ID (n = 20). Caregiver ratings of the compulsive behavior checklist were compiled. Data were analyzed using qualitative content analysis. Results: All forms of OCD were present. Characteristics of compulsive behaviors in people with ID at the behavioral level included less complex and more obvious compulsive acts, immediate responses, signs of tension, motor restlessness, facial expression changes, repetition, need for predictability, time-consuming behaviors, and aggressive reactions when these acts were interrupted. Some of the compulsive behaviors corresponded to the ICD-11 OCD code 6B20, and others to compulsions as a psychological symptom (MB23.4). Conclusions: OCD may manifest atypically at the behavioral level in people with ID, posing significant challenges for accurate classification due to symptom ambiguity. Follow-up differential diagnostic studies are needed to more accurately identify and differentiate OCD symptoms in people with ID. Further, disorder-specific guidelines for recognizing OCD in people with ID are needed for institutionalized settings without psychiatric-psychotherapeutic expertise.