OBJECTIVES: The 3-year Diabetes Prevention Program (DPP) and 7-year follow-up Diabetes Prevention Program Outcomes Study (DPPOS) demonstrated that both intensive lifestyle interventions (ILI) and metformin led to reductions in the incidence of type 2 diabetes (T2D) versus standard care (control) in overweight or obese subjects with impaired glucose tolerance (IGT). Our aim was to project the long-term cost-utility of T2D prevention in an Australian setting, based on clinical results and resource utilization from the DPP+DPPOS. METHODS: We developed a semi-Markov, 2nd-order Monte Carlo model to project the 10-year clinical and cost results of the DPP+DPPOS to patient lifetimes. Four health states were modelled: normoglycaemia (NG); IGT; T2D and dead. Subjects started in IGT and progressed to T2D or NG, depending on the treatment received. State-specific mortality rates for NG, IGT or T2D were used. We incorporated direct medical costs (from official Australian published sources and the reimbursement perspective) and Australian utility and probability data. Total lifetime costs (C), quality-adjusted life years (QALY) and incremental C/QALY-gained were calculated for ILI or metformin versus control. Outcomes were discounted at 5% annually. Validations and sensitivity analyses were performed. RESULTS: Delayed onset of T2D led to mean (standard deviation) QALY-gained of 0.38 (0.05) and 0.12 (0.04) years for ILI or metformin versus control, respectively. Costs savings of $282 (4,222) per patient and cost increases of $1,116 (4,338) were projected for ILI or metformin versus control, respectively. ILI was dominant to control. C/QALY-gained for metformin versus control were $8757. Probability of acceptance at a willingness to pay threshold of $50,000 were 100% and 85% for ILI or metformin respectively. Results were most sensitive to probabilities of developing T2D, and costs of implementing the interventions. CONCLUSIONS: Lifetime projection of the DPP+DPPOS results found ILI dominant and metformin to be cost-effective versus control by current Australian standards.