Aims: Type 2 diabetes is a major public health issue that has a large effect on society including its health and social services. The aims of this paper are to generate a projection of the number of cases and explore the potential impact of a preventive intervention targeted at people with pre‐diabetes on disease prevalence, complications, mortality and cost. Methods: A Markov simulation model of diabetes and pre‐diabetes in Ireland, for the period 1991 to 2036, was generated based on international epidemiological data. The simulation was calibrated with the available Irish data on the prevalence of pre‐diabetes, diabetes and diabetic complications. The economic and health impact of a hypothetical nationwide preventive intervention programme, which reduces the incidence by a factor consistent with the international literature, was estimated under three scenarios of alternative effectiveness and uptake. Results: The estimated number of people over 40 years of age with type 2 diabetes in Ireland is projected to increase from 216,000 in 2020 to 414,000 in 2036. A prevention programme, based on the NHS Diabetes Prevention Programme, is estimated to result in a reduction of between 2000 (0.5%) and 19,000 (4.6%) in the number of prevalent cases of diabetes in 2036 resulting in substantial health and quality of life benefits. Conclusions: A wide range of initiatives with uncertain outcomes will be required to reduce the impact of obesity and type 2 diabetes. A diabetes prevention programme seems likely to be worth pursuing as one element of this set of initiatives. [ABSTRACT FROM AUTHOR]