Breast feeding in infancy may be associated with reduced cardiovascular morbidity in adulthood. We examined the association between breast feeding in infancy and arterial function and structure in adulthood in a population-based cohort of Finnish adults. Noninvasive ultrasound was used to measure brachial artery flow-mediated dilatation (FMD), carotid artery intima-media thickness (IMT) and carotid artery compliance (CAC) in 1667 young adults participating in the Cardiovascular Risk in Young Finns Study with data on early nutrition. Maximal FMD was higher in breast-fed men compared to formula-fed men (7.2+/-4.0 vs 5.9+/-3.4%, P=0.029) while no differences were seen between breast-fed and formula-fed women (8.9+/-4.5 vs 8.8+/-5.0%, P=0.84). In men, the multivariable correlates of FMD included the group variable for breast feeding (P=0.014), birth weight (P=0.043), waist circumference (P<0.001) and baseline brachial artery diameter (P<0.001). In women, the multivariable correlates of FMD were birth weight (P=0.02), waist circumference (P<0.001) and brachial artery baseline diameter (P<0.001). Breast feeding was not significantly associated with IMT or CAC in multivariable models. Adult men who have been breast fed have better brachial endothelial function compared to men who have been formula fed.