Objective: To review the projected long term costs and outcomes of continuous subcutaneous insulin infusion (CSII) compared with multiple daily injections (MDI) of insulin in adult type 1 diabetes mellitus (T1DM) patients in the USA, Canada (CAN), Australia (AUS), and the United Kingdom (UK). Methods: A valid health economic model was used to determine the incremental cost-effectiveness ratio (ICER) of CSII compared with MDI among adult patients with T1DM for all four countries. The primary input variable was change in HbA1c and was assumed to be a -1.2% improvement for CSII vs. MDI. A series of Markov constructs simulated the progression of diabetes-related complications. The average annual costs for CSII compared with MDI were locally derived (a 7-8 year pump life was assumed). The costs of optimal drug therapy, procedures and complications were derived from published federal and industry specific data. A 60-year time horizon was used for all analyses and a discount rate of either 3.0% (USA, UK) or 5.0% (CAN, Australia) per annum on costs and clinical outcomes were used. Results: Treatment with CSII vs. MDI was associated with an improvement in quality-adjusted life years (QALYs) gained of 1.061, 0.655, 0.467 and 0.760 for adults in the USA, CAN, AUS and the UK, respectively. ICERs were USD$16,992, CAN$23,797, AUS$74,147 and £25,648 per QALY gained for CSII vs. MDI in adults with T1DM. Improved glycemic control from CSII treatment led to a lower incidence of diabetes complications; most prominently for proliferative diabetic retinopathy, end stage renal disease and peripheral vascular disease. Conclusion: Setting the willingness to pay at the accepted level for each country (USD$50,000/QALY, CAN$50,000/QALY, AUS$76,000/QALY and £30,000/QALY), the analyses demonstrated that CSII is a cost-effective treatment option for all four countries when compared to MDI for adult TIDM patients.