BACKGROUND AND AIMS: The European 'IMMIDIET' study was designed to evaluate the effect of genetic and dietary habit interactions on cardiovascular disease risk factors in non-diabetic subjects. Copper, zinc and selenium are involved in redox balance and modifications of their homeostasis could be associated with metabolic syndrome. Because few studies have dealt with trace element status in metabolic syndrome with conflicting results, we aimed at investigating the relationships between plasma copper, zinc and selenium concentrations and metabolic syndrome in the IMMIDIET population. METHODS AND RESULTS: Male-female couples born and living in Abruzzo, Italy (n = 271); Limburg, Belgium (n = 267), southwest part of London, England (n = 263) and 205 Italian-Belgian mixed couples living in Belgium were enrolled. Data on medical history, hypertension and blood lipid profile, medication use, smoking and alcohol habits, physical activity and socioeconomic status were collected using a standardised questionnaire. Anthropometric, blood pressure, glucose, insulin, lipid profile and copper, zinc and selenium measurements were performed. Participants were classified in two groups according to the presence of metabolic syndrome (Yes/No). Comparison between these two groups, performed separately in men and women, indicated no association in men whereas, in women, metabolic syndrome was associated with higher plasma selenium concentrations (odds ratio (OR) = 1.55(1.28-1.89)); this association remained significant after adjustment for age, group, social status, physical activity, energy intake, alcohol consumption, smoking and hormonal status (OR = 1.33 (1.06-1.67)). CONCLUSION: Our results indicate gender differences in the association between plasma selenium concentration and metabolic syndrome without diabetes and may suggest a sub-clinical deleterious effect of high selenium status in women.