Comorbid physical health conditions, commonly associated with mental illness, contribute to increased morbidity and reduced life expectancy. The trajectory to poorer health begins with the onset of mental illness. For young people with mental illness, health risk behaviours and poor physical health can progress to adulthood with long-term detrimental impacts. Using a cross-sectional survey design, self-reported health risk behaviours were gathered from 56 young (16–25 years)Australians who had been hospitalized for mental illness and taking psychotropic medication. Smoking, alcohol use, minimal physical activity, and lack of primary health care were evident. While these behaviours are typical of many young people, those with mental illness have substantially increased vulnerability to poor health and reduced life expectancy. Priority needs to be given to targeted health promotion strategies for young people with mental illness to modify their risky long-term health behaviours and improve morbidity and mortality outcomes. Nurses in mental health settings play a vital role in promoting young peoples’ well-being and preventing poorer physical health outcomes. Implementation of a cardiometabolic health nurse role in inpatient settings for young people with mental illness could facilitate prevention and early intervention for health risk behaviours.