BACKGROUND The relation between smoke exposure in early life, the prenatal period in particular, and the vascular development of young children is largely unknown. METHODS Data from the birth cohort participating in the WHISTLER-Cardio study were used to relate the smoking of parents during pregnancy to subsequent vascular properties in their children. In 259 participating children who turned 5 years of age, parental smoking data were updated and children's carotid artery intima-media thickness (CIMT) and arterial wall distensibility were measured by using ultrasonography. RESULTS Children of mothers who had smoked throughout pregnancy had 18.8 μm thicker CIMT (95% confidence interval [CI] 1.1, 36.5, P = .04) and 15% lower distensibility (95% CI -0.3, -0.02, P = .02) after adjustment for child's age, maternal age, gender, and breastfeeding. The associations were not found in children of mothers who had not smoked in pregnancy but had smoked thereafter. The associations were strongest if both parents had smoked during pregnancy, with 27.7 μm thicker CIMT (95% CI 0.2, 55.3) and 21% lower distensibility (95% CI -0.4, -0.03). CONCLUSIONS Exposure of children to parental tobacco smoke during pregnancy affects their arterial structure and function in early life.