Evidence is presented that children in foster care are more likely to show uncharacteristic patterns of cortisol production (a steroid hormone secreted by the adrenal cortex as part of the body’s response to stress) across the day than children who have not experienced foster care. Children entering foster care in infancy showed uncharacteristic patterns of cortisol across the day relative to comparison children. These differences suggest that conditions associated with foster care interfere with children’s ability to regulate neuroendocrine functioning (relating to the nervous and endocrine systems). There are a number of factors that could lead to agitations in the regulation of cortisol production in addition to foster care placement itself. Young children placed into foster care differ from children who are not placed into foster care in the early environments to which they have been exposed. Neglect and maltreatment have been linked with different patterns of cortisol production. Young children who are placed into foster care have been found to experience inadequate care and/or separations from caregivers at a key biological developmental point. Studies suggest that early inadequate care and separations are associated with long-term changes in regulation of the Hypothalamic-pituitary-adrenal (HPA) axis. The study consisted of 55 young children (age 20 to 60 months) placed in foster care and 104 who had not . Average salivary cortisol values for each time of day were computed with saliva samples taken at wake-up, in the afternoon, and at bedtime for 2 days. Figures, table, references