Epidemiological research has suggested that mental disorders are risk factors for the subsequent development of some chronic physical conditions. The limitations of prior epidemiological research in this area have precluded understanding of which types of mental disorder are 'toxic', the critical periods during which they exert their effects, and which physical conditions are affected. The proposed research will address these limitations through secondary analyses, using a prospective analytical framework of the 31-country World Health Organization's World Mental Health (WMH) surveys (n=80,000). If the research hypotheses are supported, this could lead to a new understanding of the interplay of mental and physical health, with recognition of early onset mental disorders as broad spectrum risk factors for a range of chronic physical conditions. This, is turn, would provide much needed impetus for the detection and treatment of mental disorders in early life, both for their own sake and for the sake of their lifelong impact on physical health.