OBJECTIVE: To determine the association between socio-economic status (SES) and risk of hand, hip or knee osteoarthritis at a population level. DESIGN: Retrospective ecological study using the SIDIAP database (primary care anonymized records for > 5 million people in Catalonia (Spain)). Urban residents > 15 years old (2009-2012) were eligible. OUTCOMES: Validated area-based SES deprivation index MEDEA (proportion of unemployed, temporary workers, manual workers, low educational attainment and low educational attainment among youngsters) was estimated for each area based on census data as well as incident diagnoses (ICD-10 codes) of hand, hip or knee osteoarthritis (2009-2012). Zero-inflated Poisson models were fitted to study the association between MEDEA quintiles and the outcomes. RESULTS: Compared to the least deprived, the most deprived areas were younger (43.29 (17.59) versus 46.83 (18.49), years (Mean SD), had fewer women (49.1% versus 54.8 %), a higher percentage of obese (16.2 % versus 8.4 %), smokers (16.9 % versus 11.9%) and high-risk alcohol consumption subjects (1.5% versus 1.3 %). Compared to the least deprived, the most deprived areas had an excess risk of osteoarthritis: age-sex-adjusted IRR 1.26 (1.11-1.42) for hand, 1.23 (1.17-1.29) hip, and 1.51 (1.45-1.57) knee. Adjustment for obesity attenuated this association: 1.06 (0.93 -1.20), 1.04 (0.99-1.09), and 1.23 (1.19-1.28) respectively. CONCLUSIONS: Deprived areas have higher rates osteoarthritis (hand, hip, knee). Their increased prevalence of obesity accounts for a 50% of the excess risk of knee osteoarthritis observed. Public health interventions to reduce the prevalence of obesity in this population could reduce health inequalities