OBJECTIVE Limited data suggest that people with the metabolic syndrome have lower intakes or circulating concentrations of magnesium than those who do not have the syndrome. The aim of this study was to examine the associations between dietary intake of magnesium and the prevalence of the metabolic syndrome in a nationally representative sample of U.S. adults. METHODS We used data for 7669 participants > or =20 years of age of the Third National Health and Nutrition Examination Survey (1988 to 1994). The metabolic syndrome was defined using the criteria of the National Cholesterol Education Program. Magnesium intake was determined from a single dietary 24-hour recall. RESULTS The unadjusted prevalences of the metabolic syndrome were 29.0% (quintile of lowest magnesium intake), 27.5%, 25.8%, 23.9%, and 21.8% for increasing quintiles of magnesium intake (p for trend = 0.002). After multiple adjustment, the odds ratios for the second through the fifth quintiles (highest intake) of magnesium intake among all participants included in the analysis were 0.84 [95% confidence interval (CI): 0.58, 1.23], 0.76 (95% CI: 0.54, 1.07), 0.62 (95% CI: 0.40, 0.98), and 0.56 (95% CI: 0.34, 0.92), respectively (p for trend = 0.029). The associations were similar for men and women. CONCLUSIONS Our results showing an inverse association between dietary magnesium intake and the prevalence of the metabolic syndrome add to the evidence that adequate magnesium intake or a diet rich in magnesium may be important for maintaining good cardiometabolic health.