AIMS: To describe insulin therapy in patients with diabetes, to determine treatment costs and to compare costs among treatment regimens. METHODS: This observational study was performed by 734 French pharmacists. Adult patients filling an insulin prescription were invited to participate. Participants provided information on their diabetes history and management. Levels of intensification of insulin therapy were determined by the number of injections in type 1 diabetes mellitus (T1DM) patients, and by the different schemes used in type 2 (T2DM) patients, such as basal/intermediate-acting insulin only, and regimens using both basal and rapid-acting insulin. Costs were evaluated according to official medication costs, nurse visits and glucose monitoring kits. RESULTS: A total of 361 patients with T1DM and 1902 with T2DM were enrolled in the survey. Patients with T1DM more frequently took 1-2 injections per day (46.3% of patients) and used single-dose basal insulin together with ≥1 dose of rapid insulin (43.8%). Patients with T2DM used multiple treatment regimens, with 58 different combinations documented. Most took basal/intermediate insulin only (42.5%) or combinations of basal/intermediate and rapid insulins (52.7%). Mean cost of insulin therapy was €27.4/week for T1DM and €45.4/week for T2DM. In T1DM, insulin was the biggest cost component and increased with the number of injections/day. In T2DM, nurse visits were the most important cost contributors irrespective of treatment regimen. Overall, the cost of insulin therapy increased with the complexity of the insulin schemes. CONCLUSION: Considerable heterogeneity is found in insulin treatment regimens used in everyday diabetes care. Payers should consider the full costs associated with the use of insulin rather than the cost of insulin alone. Treatment algorithms to harmonize insulin therapy should help to improve care, while encouraging patients to self-inject insulin should help to reduce costs.