OBJECTIVES: This retrospective study compares annual expenditures among T2DM patients according to treatment stage and renal function status (RFS) and identifies determinants of costs. METHODS: T2DM patients’ records were extracted from the EGB database, which contains ambulatory care claims for a representative sample of the French population. Patients were classified according to treatment stage: oral / GLP1 monotherapy, double therapy, triple therapy or insulin therapy (either associated or not with other antidiabetics), and according to RFS (identified using pharmacy, lab and consultation claims). Costs were estimated from the national insurance perspective and included all reimbursements except for hospitalisations. Annual expenditures were assessed by year (from 2005 to 2010), by treatment stage and by RFS. Effects of treatment stages and RFS on expenditures by year were analysed by means of generalised linear models, with matching on age and gender. RESULTS: The number of patients ranged from 9,682 to 11,772 between 2005 and 2010. Annual average total reimbursements in 2010 were €3,279 (standard error: 65.5) for monotherapy, €3,592 ±92.1 for double therapy, €3,803 ±157.2 for triple therapy and €7,729 ±180.8 for insulin therapy. The same cost pattern was found in previous years. The regression model showed that costs increased by a ratio of 2.31 (p<0.001) from monotherapy to insulin therapy, adjusted for socio-demographic characteristics and co-treatments. Excess costs for insulin therapy were mainly related to nursing care (increasing by a ratio of 12.16, p<0.001), medical devices and pharmacy costs. Reimbursements for patients with declining renal function were estimated at €4,933 ±368.9 for monotherapy, €4,521 ±350.8 for double therapy, €4,191 ±497.9 for triple therapy and €13,768 ±1106.2 for insulin therapy. CONCLUSIONS: Overall, ambulatory care costs increase with treatment escalation and declining renal function amongst T2DM patients. Insulin therapy is associated with substantial increased costs, related to pharmacy, nursing care and medical device utilization.