We examined predictors of stability and decline in activities of daily living (ADLs) and mobility in a population-based sample of the oldest old. Respondents were people aged 84 to 90 living in South Central Sweden. Predictors were drawn from three domains: sociodemographic variables, vitality, and physical and psychological health. Using a logistic regression model, we sought to identify variables that were associated with changes in functioning. Over the 2-year interval, we found significant main effects for stability in ADL functioning for three variables: residential status (e.g., living in the community), subjective health, and mastery (n = 142). For mobility, we identified three variables associated with stability: lung function, subjective health, and mastery (n = 137). Over the 4-year period we found that residential status was significantly associated with stability in ADL performance (n = 89), while age, marital status, grip strength, and mastery were significant predictors for stability in mobility (n = 90). The findings can direct researchers toward interventions within particular residential environments that maintain a sense of mastery and an individual's aggressive attitude toward challenging situations.