The metabolic syndrome (MetS) is a cluster of metabolic abnormalities in which visceral obesity is a prominent feature. Although a matter of debate, the MetS essentially represents "at risk obesity." The purpose of this study was to compare the various definitions of MetS, with a special focus on abdominal obesity, and to explore sex and ethnic differences in the prevalence and nature of this syndrome in 3 ethnic groups residing in the Canadian province of Québec. The study population included adult participants of 3 cross-sectional health surveys conducted in southern Québec, James Bay, and Nunavik between 1990 and 1992. A total of 2613 adults (18-74 years old) were included: 1417 Quebecers, 817 Indian Crees, and 379 Inuit. The prevalence of MetS varied by definitions, and the highest agreement was observed between the National Cholesterol Education Program-Adult Treatment Panel III and the International Diabetes Federation (79%). Most women (25%), regardless of ethnic origin, presented with a "triad" profile characterized by high waist circumference, elevated triglycerides, and low high-density lipoprotein, whereas 20% of men had the "deadly quartet" of high blood pressure with the triad mentioned above. Furthermore, our results highlight an obvious difference in the impact of the increased abdominal obesity on metabolic parameters such as insulin resistance measured by the homeostasis model assessment according to ethnic origin (P < .001). These 3 unique population-based samples suggest that abdominal obesity does not have a similar deleterious impact according to ethnicity, suggesting the need for an ethnic-based MetS definition.