A stressor above a threshold magnitude, or multiple stressors applied simultaneously, cause an organism to alter its behaviour and physiology, with the aim of maintaining homeostasis. The adaptive changes that occur are coordinated and mediated by the stress system in the central nervous system (which includes corticotrophin-releasing hormone and noradrenergic neurons in the hypothalamus and brainstem, respectively), and its peripheral limbs, the hypothalamic-pituitary-adrenal axis and the autonomic (sympathetic) system. Controlled or self-driven challenges to homeostasis and a normally functioning stress system are crucial for normal development and preservation of self and species. In childhood and adolescence, appropriately functioning neuroendocrine responses to stressors are necessary to allow growth and psychosexual maturation to progress normally. Maladaptive neuroendocrine responses, i.e. dysregulation of the stress system, may lead to disturbances in growth and development and cause psychiatric, endocrine/metabolic and/or autoimmune diseases or vulnerability to such diseases, not only during childhood and adolescence, but also in adulthood.