To estimate the short-term (1 year) cost-effectiveness of Insulin Detemir (IDet) compared with Neutral Protamine Hagedorn (NPH) insulin for Type 1 (T1DM) and Type 2 Diabetes Mellitus (T2DM) in Portugal. Methods: A short-term cost-effectiveness model was adapted to the Portuguese National Health System (NHS), to estimate the Incremental Cost-Effectiveness Ratio (ICER) of IDet vs. NPH in terms of euros per quality-adjusted life years (€/QALY) gained. Non-severe hypoglycemia (NSH) rate for both diabetes types, and weight change, only for T2DM, were the clinical benefit variables. Three scenarios were estimated in which NPH was assigned three different values corresponding to a cohort of recent insulinization and a cohort of long-run insulinization from the UK Hypoglycemia Study and from a Spanish observational study. For all scenarios, the hypoglycemia Rate Ratio (RR) for T1DM was based on the CADTH Technology Report while for T2DM it was based on the head-to-head NCT00104182 randomized clinical trial. For T2DM, weight gain was also included in the model, based on the same RCT. Disutility values to calculate quality-adjusted life years (QALYs) were associated to NSH events and to BMI unit gain.