Despite the role of magnesium in maintaining health, much of the U.S. population has historically not consumed adequate amounts of magnesium. Furthermore, significant racial or ethnic disparities in magnesium intake exist. Our objective was to provide more recent data about magnesium intake in the U.S. population. We analyzed the 24-h dietary recall data from 4257 participants aged >or=20 y from the National Health and Nutrition Examination Survey 1999-2000. The median intake of magnesium was 326 mg/d (mean 352 mg/d) among Caucasian men, 237 mg/d (mean 278 mg/d) among African American men, 297 mg/d (330 mg/d) among Mexican American men, 237 mg/d (mean 256 mg/d) among Caucasian women, 177 mg/d (mean 202 mg/d) among African American women, and 221 mg/d (mean 242 mg/d) among Mexican American women. Among men and women, Caucasians had significantly higher mean intakes of dietary magnesium than African Americans but not Mexican Americans. Magnesium intake decreased with increasing age (P for linear trend = 0.035 for Caucasians; P for linear trend <0.001 for African Americans and Mexican Americans). Men had higher intakes of magnesium than women for each of the three race or ethnic groups (P < 0.001 in each group). Caucasian men, African American men and Caucasian women who used vitamin, mineral or dietary supplements consumed significantly more magnesium in their diets than did those who did not. Substantial numbers of U.S. adults fail to consume adequate magnesium in their diets. Furthermore, racial or ethnic differences in magnesium persist and may contribute to some health disparities.