Plant sterols (phytosterols) are a normal component of the diet. Their uptake and elimination is tightly controlled, so that only very low levels are normally found in plasma. However, rare mutations in genes responsible for phytosterol elimination lead to phytosterolemia, a condition in which circulating phytosterols attain very high levels. Phytosterolemia is associated with premature atherosclerosis, thereby suggesting that elevated absorption of phytosterols can increase the risk of cardiovascular disease. Dietary phytosterol supplementation is increasingly used to lower plasma LDL-cholesterol levels. Whether the more modest elevation in plasma phytosterols achieved with dietary supplementation in normal subjects is associated with increased risk for cardiovascular disease is uncertain. Experimental data from recent studies in animals and humans are not conclusive, and therefore more detailed studies are needed.