This article describes the development of the Resident Satisfaction Index (RSI) to measure the quality of assisted living from the residents' perspective. In total, 156 residents in 13 assisted living facilities participated in the study. Exploratory factor analysis confirmed five hypothesized RSI subscales representing resident perceptions of health care, housekeeping services. physical environment, relationships with staff; and social life/activities. Cronbach's alpha for the RSI subscales ranged from .77 to .86, and for the entire index it was .92. The correlation of the RSI with the Affect Balance Scale (ABS) was .53, providing further support for its construct validity. The instrument could be used by policy makers and professionals interested in improving the quality of life for the frail elderly in assisted living.