: BACKGROUND: Differences in the use of hip and knee replacement by sex, age, ethnicity or socioeconomic status may lead to differences in disease severity between those who have surgery. METHODS: Analyses used data collected from 117 736 patients in 2009-10 via the Patient Reported Outcome Measures (PROMs) programme in England. Adjusted differences were estimated in the Oxford Hip Score (OHS) or the Oxford Knee Score (OKS), both expressed on a scale from 0 to 48, and the proportion with longstanding problems (>5 years), expressed as odds ratios (ORs). RESULTS: Women had more severe pain and disability than men on average (difference OHS 2.3 and OKS 3.3), but less often longstanding problems. Compared with white patients, average severity was higher in South Asian patients (difference OHS 2.7 and OKS 3.0) and in black patients (difference OHS 0.9 and OKS 1.6), who also more often had longstanding problems (OR 1.40 for hip and 1.54 for knee). Patients from deprived areas had more severe disease (difference OHS 3.6 and OKS 3.3 between least and most deprived quintile). CONCLUSIONS: There is evidence that non-white and deprived patients tend to have hip and knee replacement surgery at a later stage in the course of their disease.