OBJECTIVES: To investigate whether an abbreviated five-item functional status survey consisting of five activities of daily living (ADLs) reflects changes measured over time in a full 12-item functional status survey. DESIGN: Longitudinal evaluation with mean follow-up of 11 months. SETTING: Two managed-care organizations in the United States. PARTICIPANTS: Four hundred twenty community-dwelling older people at moderate to high risk of death and functional decline enrolled in the Assessing Care of Vulnerable Elders (ACOVE) observational study. MEASURES: Number of ADL abilities according to the short (range 0-5) and full functional status surveys (range 0-12); change in function as defined according to a 1-point change in short score and 1- to 2-point change in full survey scores. RESULTS: Changes in short functional status survey scores were highly correlated to changes in long survey scores (correlation coefficient=0.88). On average, a 1-point change in the short survey score was associated with a 1.4-point change on the long survey score (P<.001). The short survey correctly classified 93% of those who declined according to the long survey, adjusting for chance agreement (kappa=0.82) and was responsive to decline in function (sensitivity 82-94%, specificity 94-97%, and area under the receiver operating curve 0.91-0.93 for 1- to 2-point decreases in full survey ADL counts). CONCLUSION: The short functional status survey is an efficient way to detect changes in functional status in vulnerable older populations for clinical and research purposes.