Objectives To describe the methods of a longitudinal cohort study among older adults with preclinical disability. The study aims to address the lack of evidence guiding mobility rehabilitation for older adults by identifying those impairments and impairment combinations that are most responsible for mobility decline and disability progression over 2 years of follow-up. Design Longitudinal cohort study. Setting Metropolitan-based health care system. Participants Community-dwelling primary care patients aged ≥65 years (N=430), with self-reported modification of mobility tasks because of underlying health conditions. Interventions Not applicable. Main Outcome Measures Late Life Function and Disability Instrument (LLFDI) (primary outcome); Short Physical Performance Battery and 400-m walk test (secondary outcomes). Results Among 7403 primary care patients identified as being potentially eligible for participation, 430 were enrolled. Participants have a mean age of 76.5 years, are 68% women, and have on average 4.2 chronic conditions. Mean LLFDI scores are 55.5 for Function and 68.9 and 52.3 for the Disability Limitation and Frequency domains, respectively. Conclusions Completion of our study aims will inform development of primary care–based rehabilitative strategies to prevent disability. Additionally, data generated in this investigation can also serve as a vital resource for ancillary studies addressing important questions in rehabilitative science relevant to geriatric care.