This chapter focuses on the immediate outcomes of unresponsive early care during infancy, including the development of non-optimal physiological stress reactions and disorganized attachment behavior. It reviews the recent research pointing to interaction between caregiving environment and gene expression in the dopaminergic and serotonergic systems, as these effects relate to maladaptation in childhood and psychiatric morbidity in adulthood. Research using animal and human models has identified associations between characteristics of the early caregiving environment and infant physiological responsiveness to stressors. Disorganized attachment patterns in infancy have been associated with childhood onset of aggressive behavior problems and with psychopathology in young adulthood. Inadequate early care is an important risk factor in human development for multiple later psychopathologies. The chapter proposes that the risk for both physiological and behavioral dysregulation as a result of poor early care in infancy constitutes a hidden trauma.