The Adverse Childhood Experiences (ACE) Study is a long term, in-depth analysis of over 17,000 adult Americans, matching their current health status against adverse childhood experiences that occurred on average a half-century earlier. We found that such adverse childhood experiences are quite common although typically concealed and unrecognized; that they still have a profound effect a half century later, although now transmutated from psychosocial experience into organic disease; and that they are the main determinant of the health and social well-being of the nation. Our findings are of direct importance to the everyday practice of medicine and psychiatry because they indicate that much of what is recognized as common in adult medicine is the result of what is not recognized in childhood. The ACE Study challenges as superficial the current conceptions of depression and addiction, showing them to have a very strong dose-response relationship to antecedent life experiences.