OBJECTIVES: To estimate the long-term clinical outcomes in type 1 diabetes patients treated with either insulin detemir (IDet) or neutral protamine Hagedorn (NPH) insulin based basal-bolus therapy in a Spanish setting. METHODS: A validated computer simulation model of type 1 diabetes (the CORE Diabetes Model) was used to make long-term projections of clinical outcomes based on patient characteristics (mean age 40.3 years, duration of diabetes 16.3 years, HbA1c 8.3%, BMI 25.2 kg.m-2) and treatment effects (HbA1c improvement of 0.13% points, a 4% decrease in hypoglycaemic events and lower body mass index of 0.21 kg.m-2 with IDet) from a fixed-effects meta-analysis of three clinical trials (n = 1555) where patients received either NPH or IDet as the basal component of therapy. Clinical outcomes were discounted at 3.5% per annum. RESULTS: IDet was projected to improve discounted life expectancy by approximately 0.082 years (14.42±0.17 versus 14.33±0.17 years) and quality-adjusted life expectancy by 0.173 quality-adjusted life years (QALY) (7.21±0.09 versus 7.04±0.08 QALYs) compared to NPH. The mean time to onset of any diabetes-related complication was delayed by 0.07 years in the IDet arm (1.11 versus 1.04 years) with the cumulative incidence (CI) of diabetes related complications over the patient lifetimes reduced. For example, the CI of end stage renal disease (ESRD) was 2.4% lower (18.3% versus 18.8%) with IDet versus NPH and, similarly, benefits were projected for proliferative diabetic retinopathy (4.4% lower, 21.7% versus 22.7%) and peripheral vascular disease (2.7% lower, 14.4% versus 14.8%). CONCLUSION: The use of IDet versus NPH was projected to lead to reduced complication costs over patient lifetimes, particularly for ESRD and retinopathy, due to improvements in glycaemic control. This is despite the survival paradox whereby IDet patients live longer than those receiving NPH and are therefore at a greater risk of complications.