An alarming proportion of adolescents engage in purposefully self-injurious behavior (SIB). SIB is a maladaptive strategy for coping with extreme tension generated in response to stress, particularly interpersonal stress. This study investigated the relation of older adolescents' SIB to the reactivity of the body's major physiological system for responding to stress, the hypothalamus-pituitary-adrenal (HPA) axis, after interpersonal stress. Adolescents' behavioral, cognitive, and emotional coping strategies were shown to alter the relation between SIB and HPA reactivity after conflict with a romantic partner.