The severity or algofunctional indices for hip and knee osteoarthritis (OA) have been used in Europe for about 10 years. They were validated, then published between 1982 and 1987. They are useful mainly as outcome measures in OA trials, and also for appraising the severity of patient function: a score above 11-12 points after appropriate treatment indicates surgery. Most patients recruited in OA trials have a score of 9-11 (SD 2.3 to 3.8), decreasing about 30 to 40% with the active drug. The effect size reaches 1.3 to 1.8. The indices have 2 advantages: they are structured separately for hip and for knee OA and the same instrument serves as a measure of severity (disability scale) and as an outcome measurement tool in trials.