The past decade has seen a notable increase in interest in and research concerning the physiological correlates of behavior problems in childhood. The present article reviews what this growing body of research has revealed. The main tenet is that disruptions in both sympathetic and adrenocortical regulation appear to be common among children with internalizing and externalizing behavior problems. The associations between such neuroendocrine alterations and behavior are discussed and their implications for the fields of stress physiology, neuroendocrinology, and developmental psychopathology are outlined. It is proposed that substantial advances can be made by investigating patterns of physiological responses among multiple, concurrent systems rather than individual response systems.