The EuroQoL EQ-5D and MOS SF-36 are two generic Quality of Life measures that differ significantly in their design (the former being an index and the latter a profile). Both have been extensively used in evaluating interventions in acute disease. This study tested their comparative performance in a survey of patients with relapsing-remitting multiple sclerosis (MS). METHOD: 309 patients with diagnosed relapsing-remitting MS were identified through the records of 5 specialist centres in North West England. Patients were contacted by telephone by a specialist MS nurse and asked to complete a set of questionnaires distributed by mail. The questionnaire booklet reproduced the English version of SF-36, together with the EQ-5D and a self-completion form of the Barthel. Minimal additional background information was obtained from all respondents. 4 weeks following their completion of the initial booklet, a second identical booklet was sent to the first 200 initial respondents. Patients in this re-test sub-group were asked whether their health status had improved, deteriorated or remained unchanged over the intervening period. RESULTS: Of the 200 patients in the test/re-test sub-group, 144 (72%) replied on both occasions. Paired t-tests for the PCS, MCS and general health perception scores on the SF-36 failed to generate comprehensive evidence of reliability. The weighted index form of the EQ-5D and the visual analogue scale self-ratings provided superior evidence of reliability. Standardised response means for both measures confirmed this general pattern. CONCLUSION: EQ-5D performs satisfactorily as a generic measure of health-related quality of life in patients with MS.