Adopted individuals have an increased risk for a variety of psychopathological disorders. Studies of the effects adoption in humans are difficult to perform because of the difficulty separating genetic risk and treatment effects. This is a developmental study investigating the effects of at birth adoption using a nonhuman primate model. Three experimental paradigms were used to assess maternal treatment, stress-related behavior, and physiology late in infancy and again later in life. Rhesus monkeys were reared for their first six months of life by either their biological mother or an unrelated, lactating adult female. Adoptions occurred immediately following birth. At six months of age, both groups were exposed to four, 4-day mother-infant separations. Behavioral observations and plasma stress hormones were used to compare the two group's responses to the separation stressor. Maternal treatments were also compared. In a second experiment performed about three years later when subjects were adolescents or young adults, an unfamiliar intruder was placed outside their home pen and stress-related behavioral responses were again measured. In the third experiment, adolescent subjects were allowed free access to a sweetened alcohol solution and daily alcohol consumption was measured across 8-10 weeks. Analyses showed that adopted subjects exhibited more behavior withdrawal and higher ACTH during the Acute and Chronic phases of the separation than infants reared by their biological mothers. This persisted when subjects were again tested with an intruder stressor 1-3 years later, with adopted subjects still showing more behavioral withdrawal during the Intruder Challenge stressor. Adopted subjects also differ in their relationship with their mother, showing more independence at an early age in non-stressful environments. Paradoxically, alcohol intake was lower in adolescents raised by an adoptive mother. Differences in maternal treatment and mismatches in temperament between the adopted mother and her infant are potential mechanisms that lead to the increased stress and anxiety in subjects raised by an adopted mother.