BACKGROUND High prevalence and chronic complications are key determinants of management costs of Diabetes Mellitus (DM). Given that DM affects more than 4 million people in Spain, the costs associated with this disease require an efficient management. Cardiovascular diseases are complications associated with DM with a major impact in health care budgets. OBJECTIVES Develop a model to predict future costs of DM in Spain. Estimate the increase in health care costs in DM patients associated with potential cardiovascular diseases. We used the perspective of the Regional Health Service in Madrid (public payer). METHODS Foro Gerendia is an initiative constituted by health care professional, experts in DM management. A Markov model for DM was developed based on the opinion of Foro Gerendia and on previous works in this area. A 5-year primary care data registry of 22700 diabetic patients in Madrid was used to estimate transition probabilities in the model. Time horizon was 10 years. Prices were taken from the health care tariffs published by the Regional Health Service in Madrid and from Spanish literature. They were updated to 2013 price levels and adjusted to subsequent years by a 3% inflation rate. RESULTS Cardiovascular complications included in the model were ischemic heart diseases (acute myocardial infarction and angina) and heart failure with a total of 5 health states. The estimated increase in costs was € 1,080 per patient in 10 years (€ 108 per year). Considering an 8% prevalence of DM in Madrid, the increase in costs of DM due to cardiovascular diseases would be € 52 million per year. CONCLUSIONS Cardiovascular diseases in DM patients have a relevant impact on health care expenditure. Prevention of cardiovascular complications can lead to significant cost savings for the management of DM. Understanding future costs of DM might be valuable in terms of budget allocation and economic evaluation.