Objectives: To compare the judgments of clinicians on which domains of health in the short form questionnaire (SF-36) would be most important to patients with multiple sclerosis with the opinions of patients themselves; to compare assessment of physical disability in multiple sclerosis by a clinician using Kurtzke's expanded disability status scale and a non-clinically qualified assistant using the Office of Population Census and Surveys' (OPCS) disability scale with self assessment of disability and other domains of health related quality of life by patients using the SF-36 and the EuroQol questionnaire; and to compare the scores of patients for each domain of the SF-36 with control data matched for age and sex. Design: Cross sectional study. Setting: Clinical department of neurology, Edinburgh. Subjects: 42 consecutive patients with multiple sclerosis attending a neurology outpatient clinic for review or a neurology ward for rehabilitation. Main outcome measures: Scores on the SF-36; EuroQol; Kurtzke's expanded disability status scale; the OPCS disability scale. Results: Patients and clinicians disagreed on which domains of health status were most important (χ2=21, df=7, P=0.003). Patients' assessment of their physical disability using the physical functioning domain of the SF-36 was highly correlated with the clinicians' assessment (r=-0.87, Pr=-0.90, PConclusions: Patients with multiple sclerosis, and possibly those with other chronic diseases, are less concerned than their clinicians about physical disability in their illness. Clinical trials in multiple sclerosis should assess the effect of treatment on the other elements of health status that patients consider important, which are also affected by the disease process, are more closely related to overall health related quality of life, and may well be adversely affected by side effects of treatment. Patients can accurately assess their own physical disability Physical disability may not always be the main determinant of overall health related quality of life Patients and clinicians differ in their assessments of the relative importance of different elements of health related quality of life The opinions of patients should be taken into account in the selection of outcome measures for clinical trials