OBJECTIVES: To quantify and compare annual resource use and costs over time among Swedish patients with type 2 diabetes first treated with oral antidiabetic (OAD) medication alone and who subsequently initiated insulin treatment. METHODS: The study was based on data from the Real-Life Effectiveness and Care Patterns in Diabetes Management (RECAP-DM) study, a retrospective, population-based study on patients with type 2 diabetes identified in electronic patient records from 26 primary care centers in Uppsala county. Patients treated with OAD alone the year prior to insulin initiation in 2001-2003 were identified. Resource consumption was available from the patient records and the resource items included were visits to General practitioners (GP) or nurses at Primary care settings, visits to acute physician and visits at outpatient clinics and inpatient days. The annual costs were calculated by multiplying quantities of resource use by unit costs from a previous study and from the price list of Uppsala University Hospital. RESULTS: A total of 397 patients with type 2 diabetes were identified that initiated insulin treatment 2001-2003 after only receiving OAD. The annual resource use for diabetes nurse visits, visits to outpatient clinics and inpatient days increased significantly for patients during the year after insulin initiation compared to the year prior to insulin initiation when the patient received OAD alone. Even if annual resource use and costs for GP-visits decreased significantly (p<0.05) during the same period, total costs and the costs of diabetes nurse visits and inpatient days increased significantly the year at and the year after insulin initiation compared to the year when the patient received OAD alone (costs for inpatient days p<0.1). CONCLUSIONS: Patients initiating insulin treatment after receiving OAD alone consumes significantly more annual resources. Annual mean costs also increase significantly, driven by the increased costs of inpatient days and diabetes nurse visits.