Although there are general assumptions that physiological and behavioral indices of emotion are interrelated, empirical research has revealed inconsistent findings with regard to their degree of association, particularly in children. Two studies were conducted to examine the relations between cardiovascular reactivity and emotional behavior. In the first study, 3- to 6-year-olds completed challenging tasks during which measures of their physiological responses and facial expressions were obtained. With age, children's heart rate decreased, vagal tone increased, and facial expressions became slightly more exaggerated. However, children's physiologic reactions were unrelated to their concurrent facial expression when all children were considered, when only boys were considered, and when children extreme in their physiologic reactions were considered. Only among girls was physiologic reactivity moderately associated with concurrent negative expressiveness. In the second study, 4- and 5-year-olds' physiologic reactivity was examined as a predictor of later overt emotional reaction to venipuncture episodes. Children's overt emotional reactions were consistent across repeated venipunctures, and girls were more visibly distressed than boys. As in the first study, physiologic reactivity was generally unrelated to children's behavioral responses. Findings have implications for assumptions about the degree of coupling between biological and behavioral emotional systems in childhood.