BACKGROUND Approximately 39% of children aged <5 y in developing countries are growth retarded (stunted) and many have poor mental development and behavioral abnormalities. Animal research suggests that an altered stress response may contribute to the negative outcomes following undernutrition. OBJECTIVE We tested the hypothesis that stunted children have higher salivary cortisol concentrations and heart rates and altered behavior when compared with nonstunted children when social background was controlled for. METHODS We compared 30 stunted with 24 nonstunted children, all of whom were 8-10 y old and lived in the same poor areas of Kingston, Jamaica. All subjects were participants in a prospective, longitudinal, case-control study of children who were stunted in early childhood. We administered a test session (including psychologic and physical stressors), measured baseline and response levels of salivary cortisol and heart rate, and observed behavior. RESULTS Compared with nonstunted children, stunted children had higher salivary cortisol concentrations (P = 0.007), had higher heart rates during the psychologic test session (P = 0.03), exhibited enhanced cardiovascular responsivity to a physical stressor (P = 0.04), vocalized less, were more inhibited, and were less attentive. After birth weight or social background and maternal and child intelligence quotients were controlled for, the differences in cortisol concentration and cardiovascular reactivity remained significant. CONCLUSIONS Our findings suggest that consistent growth retardation since early childhood affects physiologic arousal, which, we speculate, may contribute to the poor cognitive functioning and immune responses of stunted children and the relation between adult short stature and increased cardiovascular risk.