OBJECTIVES: In Spain there are several pharmaceutical products for the treatment of type 2 diabetes mellitus (DM2), with different profiles which implies alternative patterns of administration. A comparative study comparing annual costs linked to the treatment with Glargine insulin (GI) and Detemir insulin (DI) has been performed with the Spanish National Health System perspective. METHODS: Clinical data related with each treatment derives, mainly, from a study performed by Rosenstock et.al (2006): a 52-week open-label, parallel, multinational trial, which compares efficacy and safety of GI and DI. This trial has shown that patients treated with GI required less dairy dose of insulin and suffer from less severe hypoglycaemia than those patients treated with DI. Data about other use of related medical resources (consumption of needles and blood glucose tests, and management of major hypoglycaemic episodes) has been obtained from Spanish published literature. Costs calculations refer to year 2007 and have been derived from Spanish databases and published tariffs. RESULTS: Patients treated with ID require 65% more dose than those treated with GI, and suffer more major hypoglycaemic events. In patients with DM2 management with GI has lower total costs than DI, which allows savings up to 534.96€ per patient-year. Savings are related with costs of total insulin, needles and blood glucose tests and also medical management required in case of major hypoglycaemic events. CONCLUSION: For patients with DM2 treatment with GI is an efficacious and safe therapeutic option compared with DI, because GI is associated with lower annual total costs, and allows saving up to 534.96€ per patient-year i.e. a 34% saving per patient-year.