OBJECTIVE To evaluate the validity of the Cumulative Illness Rating Scale (CIRS) in a geriatric institutional population by examining its associations with mortality, hospitalization, medication usage, laboratory findings and disability. METHODS A validation of the CIRS using self- and physician-report surveys, with archival data drawn from medical charts and facility records. METHODS Long-term care facility with skilled nursing and congregate apartments. METHODS Four hundred thirty-nine facility residents selected on the basis of completeness of self-report data and physician ratings. METHODS Composite measures of illness severity and comorbidity, based on physicians' CIRS ratings; time to death or acute hospitalization after assessment; medication use, drawn from pharmacy records; medical chart data on laboratory tests; self-reported functional disability. RESULTS CIRS illness severity and comorbidity indices, as well as individual CIRS items, were significantly associated with mortality, acute hospitalization, medication usage, laboratory test results, and functional disability. The CIRS showed good divergent validity vis a vis functional disability in predicting mortality and hospitalization. CONCLUSIONS The CIRS appears to be a valid indicator of health status among frail older institution residents. The illness severity and comorbidity composites performed equally well in predicting longitudinal outcomes. Item-level analyses suggest that the CIRS may be useful in developing differential illness profiles associated with mortality, hospitalization, and disability.