Aims: To assess the associations of type and duration of infant feeding with c omponents of the metabolic syndrome in children aged 9 and 15. Methods: A total of 2192 randomly selected schoolchildren aged 9 and 15 years from Estonia (n = 1 174) and Denmark (n = 1018) were studied. Insulin resistance (homoeostasis model assessment), triglyceride levels, high density lipoprotein cholesterol, and sys tolic blood pressure were measured. Results: Children who had ever been exclusiv ely breast fed had lower systolic blood pressures than those who were not. With full adjustment for age, sex, country, birth weight, pubertal stage, body mass i ndex, height, maternal and paternal education, income, smoking, and body mass in dex the mean systolic blood pressure of children who had ever been breast fed wa s 1.7 mm Hg (95%CI -3.0 to -0.5) lower than those who had never been exclusiv ely breast fed. There was a dose-response in this association with decreasing m ean systolic blood pressure across categories from never exclusively breast fed to breast fed for more than six months. Exclusive breast feeding was not associa ted with other components of the metabolic syndrome. Results were similar when e xamined separately in each country. Conclusions: The magnitude of the associatio n, its independence of important confounding factors, and the dose-response sug gest that exclusive breast feeding is causally associated with reduced systolic blood pressure. The magnitude of the effect we found with blood pressure is comp arable to the published effects of salt restriction and physical activity on blo od pressure in adult populations, suggesting that it is of public health importa nce. Aims: To assess the associations of type and duration of infant feeding with c omponents of the metabolic syndrome in children aged 9 and 15. Methods: A total of 2192 randomly selected schoolchildren aged 9 and 15 years from Estonia (n = 1 174) and Results: Children who had ever had exclusiv ely breast fed had lower systolic blood pressures than those who were not. With full adjustment for age, sex, country, birth weight, pubertal stage, body mass i ndex, height, maternal and paternal education, income, smoking, and body mass in dex the mean systolic blood pressure of children who had ever been breast fed wa s 1.7 mm Hg (95% CI -3.0 to -0.5) lower than those who had never been exclusiv ely breast fed. There was a dose-response in this association with decreasing m ean systolic blood pressure across ca tegories from never had breast fed to breast fed for more than six months. Exclusive breast feeding was not associa ted with other components of the metabolic syndrome. Results were similar when e xamined separately in each country. Conclusions: The magnitude of the associatio n, its independence of important confounding factors, and the dose-response sug gest that exclusive breast feeding is causally associated with reduced systolic blood pressure. The magnitude of the effect we found with blood pressure is comp arable to the published effects of salt restriction and physical activity on blo od pressure in adult populations, suggesting that it is of public health importa nce.