BACKGROUND: The prevalence of type 2 diabetes among Norwegian men increased from 2.6% to 3.3% from 1986 to 1997. The most important environmental risk factors for type 2 diabetes are obesity and reduced physical activity. Genetic factors are also strongly involved. Biochemical risk factors are impaired glucose tolerance and decreased insulin response. MATERIAL AND METHODS: Only a few small studies have investigated the possibility of primary prevention of type 2 diabetes. RESULTS: In a six-year intervention study on persons with impaired glucose tolerance in China, diet and/or increased physical activity reduced the risk of type 2 diabetes by 30 to 50%. Similar results were found in a study from Sweden. No drug is shown to prevent type 2 diabetes. Possible candidates are metformin and thiazolidinediones which increase insulin sensitivity, and pancreatic lipase inhibitors which reduce the absorption of fat from the gut. Three large, randomised, prospective studies are investigating whether life style intervention or medication can prevent the disease. The results of these studies will be available in about five years. INTERPRETATION: Present evidence clearly indicates that increased physical activity and diet can prevent the development of type 2 diabetes.