We evaluated the responsiveness of measures of function in admissions to a long-term care facility. Between baseline and follow-up assessment, one-fifth or more of the subjects either worsened or improved in most aspects of reported function. We compared two measures of self-reported function (COOP charts and a short-form survey). Convergent validity was observed for changes in pain, social health, and mental health (r = 0.39-0.74), but not for physical functioning. Although the short-form physical function measure discriminated worsening on several performance-based external criteria of physical functioning (area under ROC curves up to 0.82), the COOP and other measures of physical functioning were less likely to do so. All physical function measures were less responsive for detecting improvement. Clinicians and investigators intending to monitor change in function must consider the responsiveness of their measures.