The long term poor health outcomes in those who have experienced multiple adverse events in childhood have been well documented since the late 1990's. People who have experienced four or more adverse childhood experiences (ACE) are at significantly increased risk of chronic disease as well as mental illness and health risk behaviours. There is growing evidence of the ways in which adversity and toxic stress, cause these poor outcomes. Exposure to adversity has been shown to alter the molecular and genetic makeup of a child as well as changing the way the neurological, immune and endocrine systems develop and function. ACEs are of great public health concern given their long term impact on an individual's health along with the impact on society through economic factors such as loss of productivity and increasing pressure on the healthcare system. Intergenerational and environmental factors have been implicated in perpetuating the cycle of ACEs. Thus, both primary and secondary preventive intervention programmes need to be considered in firstly preventing the occurrence of ACEs and secondly striving to mitigate their ill effects. This article describes the background scientific studies, prevalence and types of risk factors and their effects on human biology and goes on to outline how ACEs contribute to later adult health status and how we might mitigate these through improved primary and secondary prevention.