This pilot study was designed to evaluate the usefulness of the Functional Limitations Profile (FLP), a validated interval measure of self-report of disability, in studies of multiple sclerosis (MS). It is compared with the standard measure of disability in MS, the Kurtzke Expanded Disability Status Scale (EDSS), and the Illness Severity Score (ISS), which is an interval score derived from the EDSS. Inherent problems of all measures are discussed. On two occasions separated by 6 months, 50 MS patients were assessed prospectively by a neurologist and a psychologist, using the above measures. Validity was reflected in correlation and in agreement between measures. The FLP Physical dimension correlated significantly with the EDSS for both visits (at visit 1: r = 0.77; at visit 2: r = 0.77). Agreement between the interval measures, FLP and ISS, was satisfactory (mean difference +0.18, SD 6.8). The reliability of FLP was assessed by comparing FLP Physical dimension scores in the 30 patients who had not changed clinically between visits (EDSS change < 1.0, ISS change < 3.8). For this unchanged group the mean difference was +0.56 (SD 6.2); the 95% confidence interval (CI) was -2.87 to +1.75. For sensitivity of the FLP the 20 MS patients who had clinically changed between visits were assessed (EDSS =/> 1.0, ISS =/> 3.8). For this changed group the mean difference was -8.0 (SD 9.21); 95% CI was -12.3 to -3.69. The FLP Physical dimension in this pilot study seems to be a valid, reliable and sensitive measure of MS disability. If confirmed by larger studies it would be useful in prospective clinical studies of treatments for MS.