The Multiple Sclerosis Impairment Scale (MSIS) is a measure of accumulated deficits assessed by means of a standard neurological examination. We compared the responsiveness of the MSIS with that of the Expanded Disability Status Scale (EDSS). We reviewed 4300 records collected systematically from 1995 to 2003 and identified 534 patients who had clinically definite multiple sclerosis and had had at least two clinical assessments with a time interval of 2-5 years. The rate of deterioration was significantly higher on the MSIS than on the EDSS. The annualized change in EDSS exhibited a maximum at baseline EDSS 4 and a subsequent rapid decline at higher baseline EDSS, while the annualized change in MSIS was fairly stable over a wide middle range of baseline MSIS. The variance of the annualized change in EDSS fluctuated markedly between the baseline EDSS categories, being highest at baseline EDSS 2, while the variance of the annualized change in MSIS was stable. The study indicates that the responsiveness of the MSIS is better than that of the EDSS in terms of both magnitude and stability over the range of measurement.