A model was proposed to assess the premise that functional limitations are an intermediary stage between risk factors (e.g., sex and frequency of walking a mile), pathology/impairments (e.g., musculoskeletal problems), and the onset and course of Instrumental Activities of Daily Living (IADL) disability. Analyses were based on two random subsamples (each with n = 524) of Longitudinal Study of Aging respondents who were nondisabled at baseline (1984) and reinterviewed in 1988 and 1990. The model's central premise was supported in two ways. The main influence of age, frequency of walking, and musculoskeletal problems was on the onset of functional limitations, rather than the onset of IADL disability. And, onset of lower body functional limitations influenced future disability (1990) through its relationship with disability in 1988 and functional limitations in 1990. The results underscore the value of clinical trials which focus on minimizing functional limitations as a strategy for preventing disability.