OBJECTIVES: A multicentre, randomised, double-blind, placebo-controlled clinical trial was conducted in Japanese impaired glucose tolerance (IGT) population to evaluate the effect of preventing the development of type-2 diabetes mellitus (T2DM), and a significant effect of voglibose in preventing the development of T2DM was confirmed compared to the placebo. The objective of this analysis was to estimate the cost-effectiveness of administering voglibose in addition to standard care of diet and exercise compared to standard care alone for high-risk Japanese individuals with IGT. METHODS: An annual cycle Markov model was constructed to estimate the long-term prognosis of individuals with IGT (56-years-old), in terms of expected medical costs, and life expectancy. The Markov model consisted of five stages: normal glucose tolerance, IGT, T2DM, dialysis and death. Transition probabilities were derived from the results of the voglibose clinical trial as well as the epidemiological information. Costs included the drug acquisition cost of voglibose, IGT management cost, annual medical costs of T2DM and cost of dialysis. Effectiveness was evaluated by life expectancy. The future costs and effectiveness were discounted by 3% per year. RESULTS: Expected lifetime costs for the voglibose administration group and the standard care group were calculated at JPY718,724 (€5,380) and JPY1,365,405 (€10,220) respectively, with voglibose administration resulting in an estimated saving of JPY646,681 (€4,840). Life expectancy was calculated at 18.672 years and 18.073 years respectively, with life expectancy prolonged by 0.599 years when voglibose was administered along with the standard care. CONCLUSIONS: In order to prevent T2DM among Japanese individuals with IGT, intervention by voglibose together with the standard care for life-style modification resulted in the expectation of long-term cost-saving, as well as prolongation of life expectancy, compared to the standard care of conducting only diet and exercise therapies.