The detrimental effects of a sedentary lifestyle and poor dietary habits are having a significant negative impact on health statistics, with obesity and its attendant risks becoming a major problem in most developed nations, including Japan. Interventions which prevent or delay the development of type 2 diabetes have the potential to reduce the morbidity and mortality associated with the disease and, as a consequence, related healthcare costs. The study conducted to assess whether alpha-glucosidase inhibitor, voglibose could prevent type 2 diabetes developing in high-risk Japanese subjects with impaired glucose tolerance (IGT). 1,780 eligible subjects received standard diet and exercise therapy, and 897 were randomised to receive voglibose and 883 placebo. The study was planned for treatment to be continued until participants developed type 2 diabetes [primary endpoint; determined by bi-annual oral glucose tolerance tests (OG'Ts) as well as fasting blood glucose measured every 3 months] or normoglycaemia or for a minimum of 3 years, subject to the findings of an interim analysis. The interim analysis significantly favoured voglibose and end-of-study report involves individuals treated for an average of 48.1 weeks. Subjects treated with voglibose had a significantly lower risk for the progression to type 2 diabetes than placebo (50/897 vs 106/881: hazard ratio 0.595). Also, significantly more subjects in the voglibose group achieved normoglycaemia compared with those in the placebo group (599/897 vs 454/881: hazard ratio 1.539). Voglibose, in addition to standard care with diet and exercise, was effective in preventing the progression of IGT to type 2 diabetes and in increasing the proportion of individuals with normoglycaemia in high-risk Japanese subjects with IGT.