OBJECTIVE: To compare the relations of adiposity and body fat distribution to body mass index (BMI) in Australians of Aboriginal and European ancestry. DESIGN: Cross-sectional volunteer samples. SETTING: Australian Aboriginal communities in remote central and northern Australia, urban European Australians resident in Melbourne, Australia. SUBJECTS: Healthy Aboriginal (130 women, 120 men) and European Australians (100 women, 47 men) with a BMI<30 kg/m(2), aged 18-35 y; all women were nonpregnant. INTERVENTIONS: Anthropometric variables and resistance-using a four-terminal impedance plethysmograph-were measured. RESULTS: Aboriginal women and men were significantly shorter and weighed less than European Australians (P<0.05). Aboriginal women had a significantly larger waist circumference and waist-to-hip ratio (WHR, P<0.0005) compared to European Australian women. The sum of four skinfold thicknesses (SFT) (S4) and trunk SFT was higher in Aboriginals as compared to European Australian women (P<0.0005); however, limb SFT tended to be lower (P=0.06). On the other hand, BMI was significantly lower in Aboriginals compared to European Australian men (P=0.011), as was hip circumference (P=0.001); however, WHR was significantly (P=0.007) higher. On regression analysis, Aboriginal women and men were significantly heavier than European Australians for the same height(2)/resistance (surrogate for fat-free mass) and S4 (surrogate for subcutaneous fat); and that Aboriginal men had a significantly higher BMI (by 1.2 kg/m(2); P<0.0005) for any given S4 and height(2)/resistance values, compared to European Australian men. CONCLUSION: Aboriginal and European Australians have a significantly different body fat distribution and fat mass for a given body weight or BMI. Use of the World Health Organization recommended BMI ranges to determine weight status may be inappropriate in Australian Aboriginal people.