Diabetes mellitus is a chronic disease that has a major social impact. Proper planning for the management of patients with diabetes mellitus requires consideration of the important costs that diabetes imposes on the health system. Most of the indirect costs (lost productivity as a result of disability, absenteeism, loss of potential productive years of life), are related to diabetic complications, which greatly exceed the rest of the costs, and are also very difficult to classify in a standard manner. Direct costs (pharmacy, hospitalisation, consultations) mostly derive from healthcare strategies that aim to reduce late complications of the condition and maintain day-to-day quality of life. Therefore, it does not seem difficult to estimate pharmaceutical expenditures. The consumption of oral antihyperglycaemic agents, insulin, injection equipment and self-monitoring equipment indicates prescription tendencies and shows the influence on costs, and provides indirect information about the quality of healthcare or patients with diabetes mellitus. Over the last few years, some developed countries have shown a progressive increase in pharmaceutical expenditure on diabetic care, whereas economically depressed countries have experienced a dramatic shortage of basic medicines such as insulin. Considering the increase in consumers, and the international distribution of illnesses, both a hypothetical excess cost (related to consumerism; incurred by the health system and the diabetic population) and an irregular distribution of economic resources are evident. A co-ordinated health plan for patients with diabetes mellitus, involving the collaboration of diabetologists and epidemiologists with the pharmaceutical industry, and appropriate training measures for patients and professionals, would improve pharmacoeconomic efficiency in managing this disorder.