BACKGROUND AND AIMS: A surveillance programme on diabetes based on administrative data is being implemented in the city of Turin, Italy. The aim of this study is to assess socio-economic differences in the prevalence of diabetes in this large Italian population-based cohort. METHODS AND RESULTS: People with known diabetes resident in Turin on July 31, 2003 were identified through three data sources: the regional register of persons with diabetes, hospital discharges and prescriptions for antidiabetic drugs. Data sources were linked to the Turin population register to obtain individual data on educational level and census tract median income. Missing cases were estimated by using the capture-recapture method. We identified 34,420 persons with diabetes; prevalence adjusted for undercount was 4.91% (95% Confidence Intervals: 4.69-5.22) among men and 4.68% (4.41-5.08) among women. Age adjusted prevalence ratios between low and high educational levels were 2.32 (2.23-2.41) in men, and 3.45 (3.28-3.62) in women. Social inequalities were larger in women than in men and in people aged 21-65 years than in those age >65 years. CONCLUSION: This population-based study shows that there are socio-economic inequalities in the prevalence of the disease, particularly in women, and in young people. Our findings indicate that: (1) prevention of diabetes should be mainly focused on the socially disadvantaged strata of the population; (2) a low cost surveillance programme of diabetes using routinely collected data is feasible to better assist public health policies.