Purpose: Residential care/assisted living facilities have become an alternative to nursing homes for many individuals, yet little information exists about staffing in these settings and the effect of staffing. This study analyzed the intensity and skill mix of nursing staff using data from a four-state study, and their relationship to outcomes. Design and Methods: We obtained longitudinal data for 1,894 residents of 170 residential care/assisted living facilities participating in the Collaborative Studies of Long-Term Care. Descriptive statistics assessed the levels of direct care staff (registered nurse, licensed practical nurse, personal care aide). Regression analyses evaluated the relationship between two staffing measures (intensity measured as care hours per resident and skill mix measured as the percentage of total care hours by licensed nurses), facility characteristics, and four health outcomes (mortality, nursing home transfer, hospitalization, and incident morbidity). Results: Care hours per resident decreased with facility size (economies of scale) only for very small facilities and increased with dementia prevalence (case-mix effect). Licensed staff accounted for a greater proportion of total hours in nonprofit settings. Health outcomes did not vary by total care hours per resident, but hospitalization rates were significantly lower in facilities with higher proportions of skilled staff hours; this effect was stronger as dementia case mix increased. Implications: Current staffing levels for the outcomes analyzed meet most residents' needs. Reduced hospitalization in relation to greater use of licensed staff suggests that increased use of these workers might result in reductions in acute care expenditures. (Contains 3 figures and 4 tables.)