OBJECTIVES: A study was performed to assess the costs of diabetes mellitus type 2 considering costs for co-morbidities and diabetes related complications in Germany. The main objective of this cross-sectional study was to describe the cost structure of the treatment of diabetes mellitus type 2. The study focuses particularly on costs for oral antidiabetic treatment. METHODS: The resource utilization of a population of 201 diabetes mellitus patients with type 2 diabetes was retrospectively documented over a period of 2 years in a cross-sectional study. The documentation was performed by general practitioners (GPs) and diabetologists germanwide. Only direct costs were considered (perspective from statutory health insurances). Subgroups were analysed considering diabetes related micro- and microvascular complications. Costs were analysed taking the perspective of the statutory health insurance into consideration. RESULTS: Total costs of 201 patients suffering from diabetes mellitus type 2 amounted to DM 1, 477,061 over a period of two years, which translates into DM 7,349 per patient. Costs per year were DM 3,674 with a maximum of DM 63,915. The largest cost-driving factor is the hospitalisation representing 34.1 % of the total costs followed by drug acquisition costs (20.4 %). Patients treated with insulin cause the 3,5 times higher costs than patients treated with oral drugs. The amount of costs also correlates with the complication status and the duration of diabetes. The lowest costs are caused by patients treated with oral antidiabetic drugs and/or diet and without complications. CONCLUSION: The highest costs were caused by patients with a high complication status, a long duration of diabetes and those treated with insulin. This result emphasises the necessity of an early treatment of diabetes mellitus type 2 preventing expensive diabetes related long term complications e.g. myocardial infarction, stroke, diabetic foot lesion or dialysis.