1 SAMMENDRAG (ABSTRACT)A significant number of infants and toddlers live under condtions of non-optimal care, ranging from normal variance in parents sensitivity to severly deprived institutional rearing. There is a growing body of evidence from animal models, but also human clinical trials, suggesting that beeing exposed to unfavourable caring conditions in early life can lead to enduring impacts on brain structure and function, rendering the individual vulnerable for the development of mental illnesses. The object of this paper has been to review up-to-date literature revealing changes in the brain due to bad quality of care early in life. Addionally, there has been an aim to collect some of the existing knowledge about the mechanisms underlying these changes. Findings from rodent maternal separation paradigms has contributed with basic neurobiological knowledge of paramount importance to our current knowledge about neurohormonal and structural impacts of insufficient quality of care in early life. Among the impacts, changes to neural structures involved i the stressresponse seems to be of central importance. Studies on the human stressresponse have revealed its sensitivity to non-optimal care, even when the child receives what is considered within the normal span of caring conditions. The reactivty of the stressresponse seems to be highly dependant on the childs level of attachment security, with a secure attachment relationship acting as a powerful buffer towards increased stress reactivity.A growing body of data from clinical trials on children naturally exposed to a variety of early relational stressors indicates that this kind of stress is associated with neurobiological changes rendering the individual vulnerable for mental disease. Many of the changes seen are comparable to changes found among the adult population with anxiety- and affective disorders. Among adults, these kind of illnesses typically become manifest after a period of acute or chronic adversities. Thus, it’s reasonable to suspect that poor caring conditions early in life renders an individual vulnerable for the effects of stress later in life, predisposing for the development of a variety of psyciatric disorders. Changes in brain structure and function, stress-responsive neurocircuits in particular, may thus bridge the gap between early traumatic experiences and the development of anxiety and affective disorders.Knowledge about how disturbances in caregiving pave the way for enduring changes in brain structure and function as well as the mechanisms leading to those kind of changes is of paramount importance to our ability to invent new strategies for prevention and treatment of these types of disorders.