This paper describes a behavior pattern in adult female cynomolgus monkeys that has several behavioral and physiological characteristics in common with human depression including reduced body fat, low levels of activity, high heart rate, hypothalamic-pituitary-adrenal (HPA) axis disturbances, and increased mortality. Under certain circumstances, this depressive behavior appears more common in socially stressed subordinate, than dominant, females. This is the first animal model of social stress-related depression in females and the first primate model of adult depression. It is important to have a female animal model of depression because women are more likely to experience a clinically significant depression than men, and depression in women is often associated with changes in reproductive system function. This model is particularly useful because these monkeys have menstrual cycles that are similar to those of women, and those that exhibit depressive behavior have relatively low levels of ovarian steroids. These monkeys may be a useful model of reproductive system-associated mood disorders in females.