OBJECTIVE: To examine the published data on the impact of westernisation on obesity, non-insulin dependent diabetes mellitus (NIDDM), and coronary heart disease (CHD) in Australian Aborigines. DATA SOURCES: Fifty-five articles from Australian and international sources (primarily peer-reviewed journals) are cited. STUDY SELECTION: Twenty-eight reports providing data on the diet, lifestyle, health and "lifestyle diseases" of Australian Aborigines before and after westernisation are included in this review. A further 27 articles on obesity, NIDDM, CHD, insulin resistance, and the impact of diet and exercise were used to help interpret the Aboriginal data. DATA EXTRACTION: Information on dietary composition, anthropometry, disease and risk factor prevalence, and relevant biochemical measurements were used for comparative and interpretive purposes. DATA SYNTHESIS: The traditional hunter-gatherer lifestyle of Australian Aborigines, characterised by high physical activity and a diet of low energy density (low fat, high fibre), promoted the maintenance of a very lean body weight and minimised insulin resistance. In contrast, for most Aborigines a Western lifestyle is characterised by reduced physical activity and an energy-dense diet (high in refined carbohydrate and fat) which promotes obesity and maximises insulin resistance. When they make the transition from their traditional hunter-gatherer lifestyle to a westernised lifestyle, Aborigines develop high prevalence rates for obesity (with an android pattern of fat distribution), non-insulin dependent diabetes, impaired glucose tolerance, hypertriglyceridaemia, hypertension and hyperinsulinaemia. The striking improvements in carbohydrate and lipid metabolism in diabetic and non-diabetic Aborigines after a temporary reversion to a traditional hunter-gatherer lifestyle highlight the potentially reversible nature of the detrimental effects of lifestyle change, particularly in young people who have not yet developed diabetes. CONCLUSION: It is suggested that insulin resistance was important to the survival of Aborigines as hunter-gatherers, but is also the underlying metabolic characteristic predisposing them to obesity, NIDDM and CHD after westernisation. Intervention strategies to prevent chronic diseases related to insulin resistance should be directed at lifestyle modification. To be effective such programmes will have to be developed and implemented at the community level.