We aimed to assess the impact of the burden and patterns of multi-morbidity on disability domains.In a cross-sectional study of 425 older adults from the Boston Rehabilitative Impairment Study of the Elderly, participants self-reported 13 chronic conditions and underwent assessment of body function (leg strength, velocity, and power, trunk extensor endurance, leg range of motion, foot sensation), activities (400 m walk test, Short Physical Performance Battery, Late Life Function and Disability Instrument (LLFDI) function scores) and participation (LLFDI-participation scores). We tested the association between multi-morbidity patterns (identified by Latent Class Analysis, LCA) and disablement measures, as well as multi-morbidity burden (captured by a multi-morbidity score) and disablement measures.LCA identified three classes - low multi-morbidity, high multi-morbidity and predominantly musculoskeletal conditions. Class membership (multi-morbidity pattern) was not associated with disablement measures, but multi-morbidity score was associated with poor performance in all domains. A 1-point higher multi-morbidity score was associated with lower scores in body functions (by 0.06 Standard Deviation (SD) unit), activities (0.07 - 0.10 SD units) as well as the participation (0.07 - 0.09 units).Multi-morbidity counts may be an excellent tool for risk stratification and identification of persons in need of rehabilitation.