A systematic review of the literature was conducted to give an overview of economic evaluations of preventive interventions in type 2 diabetes mellitus. The interventions were sorted by type of preventive intervention (primary, secondary or tertiary) and by category (e.g. education, medication for hypertension). Several databases were searched for studies published between January 1990 and May 2004 on the three types of preventive intervention. For each study selected, inclusion of specific components from a standardised list of items, including quality, was recorded in a database. Summary tables were generated based on the database.A number of conclusions were drawn from this review. The most important was that strict blood pressure control was a more cost-effective intervention than less strict control, as shown by six studies reporting cost savings to very low costs per life-year gained. Primary and secondary prevention of type 2 diabetes were also highly cost effective, but these results were based on very few studies. Medications to reduce weight and hyperglycaemia together were cost effective compared with conventional interventions. Finally, the separate results regarding medications to reduce weight, hyperglycaemia and hypercholesterolaemia varied enormously, thus no conclusion could be drawn and further economic analysis is required.