Exercise therapy is generally recommended in osteoarthritis (OA) of the hip or knee. However, coexisting disorders may bring additional impairments, which may necessitate adaptations to exercise for OA of the hip or knee. For the purpose of developing an adapted protocol for exercise therapy in OA patients with coexisting disorders, information is needed on which specific coexisting disorders in OA are associated with activity limitations and pain. To describe the relationship between specific coexisting disorders, activity limitations, and pain in patients with OA of the hip or knee, a cross-sectional cohort study among 288 older adults (50-85 years of age) with OA of hip or knee was conducted. Subjects were recruited from three rehabilitation centers and two hospitals. Demographic data, clinical data, information about coexisting disorders (i.e., comorbidity and other disorders), activity limitations (WOMAC: physical functioning domain), and pain (visual analogue scale (VAS)) were collected by questionnaire. Statistical analysis included descriptive statistics and multivariate regression analysis. Coexisting disorders associated with activity limitations were chronic back pain or hernia, arthritis of the hand or feet, and other chronic rheumatic diseases (all musculoskeletal disorders); diabetes and chronic cystitis (non-musculoskeletal disorders); hearing impairments in a face-to-face conversation, vision impairments in long distances, and dizziness in combination with falling (all sensory impairments); and overweight and obesity. Coexistent disorders associated with pain were arthritis of the hand or feet, other chronic rheumatic diseases (musculoskeletal disorders), and diabetes (non-musculoskeletal disorder). Specific disorders coexisting next to OA and associated with additional activity limitations and pain were identified. These coexisting disorders need to be addressed in exercise therapy and rehabilitation for patients with OA of the hip or knee.