It is well known that severe mental illness (such as schizophrenia, bipolar disorder and major depressive disorder) gives an increased risk for cardiometabolic diseases (including obesity, type 2 diabetes and heart disease). Recent evidence suggests that there are biological mechanisms that are shared by mental illness and cardiometabolic disease. This project will explore whether the associations between genetics, mental illness and cardiometabolic disease that we have reported in adults are already apparent in adolescents. Mental illness frequently presents during adolescence, with cardiometabolic diseases typically being diagnosed decades later. If the associations between genetics, mental illness and cardiometabolic diseases that we have observed in adults are detectable in adolescents, this research could pave the way for improved treatment of mental illness as well earlier prevention of cardiometabolic disease. Improving symptoms and slowing down progression to long term complications of mental illness has the potential to greatly enhance quality of life as well as reducing health inequalities and the healthcare costs associated with severe mental illness.