To compare the responsiveness of arthritis-specific and generic health outcome measures in relation to changes in the severity of Osteoarthritis (OA). Clinical trial patients (N=1,177) were assessed at baseline and again after two weeks of treatment. Criterion measures of change in severity included physician global assessment, knee pain on weight bearing, knee pain on motion and patient global assessment. METHOD: The responsiveness of each disease specific and generic measure was estimated independently using the relative validity (RV) methodology, which compares F-ratios for average changes in specific and generic measures across groups differing in the amount of change in the criterion variables. RV coefficients estimate how each measure responded, relative to the best measure (RV=1.0). OA-specific measures were based on the WOMAC questionnaire. Generic outcome measures included eight scales, physical and mental summary measures, and arthritis-specific health index (ASHI) scored from the SF-36 Health Survey. RESULTS: The SF-36 ASHI was most valid (RV=1.0) for 3 of the 4 clinical criteria, followed by the SF-36 bodily pain (BP) scale (RV = .74 - .98) for two of the clinical criterion. SF-36 physical health (physical functioning, role physical, physical summary) and social functioning scales were consistently more valid (RV > .30) than the SF-36 mental health scales (RV < .30). The WOMAC total scale score was more valid (RV = .91 – 1.0) than any of the three WOMAC subscales. With the exception of the SF-36 ASHI and BP scales, the WOMAC pain (RV = .80 - .83), physical functioning (RV = .76 - .95) and stiffness (RV = .61 - .70) subscales were more valid than SF-36 scales. CONCLUSION: This study replicates results from previous studies showing that arthritis-specific scoring of the generic SF-36 health profile increases its responsiveness to changes in arthritis severity.