Severe mental disorders such as bipolar disorder and schizophrenia often co-occur with chronic medical illnesses, especially cardiovascular disease and diabetes. These comorbidities are associated with a more severe course of mental illness, reduced quality of life, and premature mortality. Although the association between mental disorders and physical health complications has long been recognized, medical conditions remain undertreated in clinical psychiatric practice, and the life expectancy for individuals with serious psychiatric disorders is approximately 30% shorter than that of the general US population. Factors that are related to the mental illness (eg, cognitive impairment, reduced ability to function, and a lack of communication skills) as well as factors such as the high cost of medical care may make accessing general health care a difficult task for patients. Even when medical care is received by patients, the quality is often poor, and dangerous illnesses may be undiagnosed and untreated. In addition, harmful side effects of medications used to treat psychiatric disorders, unhealthy habits and lifestyles, and a possible genetic susceptibility to medical conditions increase the likelihood of comorbid physical conditions in patients with severe mental illness. Implementing behavioral interventions into clinical practice may help patients improve their overall health and prevent chronic medical conditions.