Objective: To evaluate socioeconomic disadvantage in prevalence, awareness and control of diabetes in universal coverage healthcare system. Methods: Data from the fifth KNHNES (2010–12) were analyzed. The sample included 10 208 individuals with diabetes aged ≥30 years. Diabetes was defined by (i) a self-reported previous diagnosis of diabetes made by a physician, (ii) the current use of oral hypoglycaemic agents and/or insulin or (iii) fasting plasma glucose ≥126 mg/dl. Subjects who were first diagnosed by the survey were classified as ‘undiagnosed’. Inadequate control was defined as HbA1c ≥6.5%. Results: It was estimated that 26.4% of subjects with diabetes were not aware of their condition and 73.1% of cases of diabetes were not adequately controlled. Inequalities in socioeconomic status were related to the diabetes prevalence in both men and women. Educational level was not predictive of diagnosis or control in men or women, whereas lower household income level was associated with diagnosis in men only. Conclusions: This widespread lack of awareness and inadequate control underscore the need for intensive efforts in these domains. Monitoring is expected to highlight the gaps in the preventive and care services offered to the most vulnerable individuals and it may induce governments and practitioners to address these issues.