OBJECTIVES: To estimate the long-term cost-effectiveness of transferring type 2 diabetes patients to an insulin detemir regimen therapy from a Neutral Protamine Hagedorn (NPH) insulin regimen in the Portuguese routine clinical practice.  METHODS: A computer simulation model “CORE Diabetes Model” was used to make long-term projections of clinical outcomes and direct medical costs based on short term findings from the European cohort in the PREDICTIVE trial. Therapy conversion to insulin detemir was associated with a reduction in glycosylated haemoglobin (HbA1c) by 0.2% (p <0.05), mean body weight was reduced by 0.7 kg (p<0.01) and the incidence of total hypoglycaemia decreased from 11.7 to 3.0 episodes per patient/year (p <0.0001). Events were projected for a time horizon of 30 years. The cost analysis takes the perspective of the Portuguese National Health System. RESULTS: Therapy conversion to insulin detemir plus OADs improves life expectancy by 0.056 years and quality-adjusted life years (QALY) by 0.462 compared to NPH insulin plus OAD. The incremental cost effectiveness ratio cost per life years gained and per QALY gained with insulin detemir plus OADs treatment as compared to NPH insulin plus OADs is 3,239€ and 393€ respectively. Type 2 diabetes complications treatment costs were the main cost driver, accounting for 67% and 77% of total direct costs of the insulin detemir therapy and NPH insulin therapy respectively. Due to a better reduction from baseline of HbA1c the development and progression of complications was delayed, and the cumulative incidence of diabetes complications decreased for insulin detemir plus OADs therapy versus NPH insulin plus OADs therapy. CONCLUSIONS: The results of this study demonstrate that insulin detemir is a very cost-effective option for the treatment of type 2 diabetes compared to NPH insulin in Portugal.