A body of literature indicates a pivotal role of magnesium in glucose homeostasis and insulin secretion and action. Studies also suggest that higher intake of magnesium may decrease blood triglycerides and increase high-density lipoprotein cholesterol levels. We prospectively examined the relations between magnesium intake and incident diabetes and metabolic syndrome in approximately 5000 Americans, aged 18 to 30 years, who were free from metabolic syndrome and diabetes at baseline. Diabetes cases were diagnosed based on plasma glucose, OGTT, A1C, and anti-diabetes medications. Metabolic syndrome was determined according to the National Cholesterol Education Program/Adult Treatment Panel III definition. Diet was assessed by an interviewer-administered quantitative food frequency questionnaire, and magnesium intake was derived from the nutrient database developed by the Minnesota Nutrition Coordinating Center. After adjustment for major lifestyle variables and other potential confounders, magnesium intake was inversely associated with incident diabetes and metabolic syndrome. Compared the highest magnesium intake group to the lowest, multivariable-adjusted hazard ratio (95% confidence interval) were 0.69 (0.52 to 0.91, P for trend < 0.01) and 0.53 (0.32 to 0.86, P for trend < 0.01) for metabolic syndrome and diabetes, respectively. In conclusion, our findings suggest that young adults with higher magnesium intake have lower risk of development of diabetes and metabolic syndrome.