Data from observational studies suggest that plasma total homocysteine (tHcy) concentration may be an independent and modifiable risk factor for cardiovascular disease (CVD) in adults. Plasma tHcy levels respond rapidly to nutrient supplementation with folic acid and vitamins Bl2 and B6, alone or in combination. The available data and the potential for prevention provide a strong rationale for understanding determinants of tHcy in youth. However, no large U.S. studies have examined the relation between tHcy levels to individuals' dietary intakes of folic acid and vitamins Bl2 and B6 in youth.