"Functional foods" supplemented with plant sterols are advertised and added to regular meals to reduce serum cholesterol concentrations. The effects of increased phytosterol levels on cardiovascular diseases, however, are not known. Findings in patients with sitosterolemia, data from epidemiological studies, and experimental data from animal studies suggest that plant sterols may potentially exert negative cardiovascular effects. Additional studies investigating relevant clinical endpoints are needed before a diet supplemented with plant sterols can be recommended in the prevention of cardiovascular diseases.