Psychiatric illnesses such as schizophrenia, bipolar disorder, major depression, obsessive compulsive disorder, or panic disorder, when coupled with a functional disability such as an inability to maintain employment or live independently, are categorized as serious and persistent mental illnesses. Although estimates vary, serious and persistent mental illness (hereafter called simply serious mental illness) is known to affect millions of U.S. adults and is a leading cause of disability. According to the National Institute of Mental Health, in a given year major depressive disorder affects 14.8 million adults, panic disorder affects 6 million, bipolar disorder 5.7 million, schizophrenia 2.4 million, and obsessive compulsive disorder 2.2 million, with many people having more than one mental disorder. People with serious mental illness are at increased risk for medical conditions such as hypertension, diabetes, heart problems, and obesity.3, 4 Reasons for this increase are related to lifestyle for example, patients with serious mental illness are more likely to smoke and less likely to engage in light or vigorous physical activity and the adverse effects of some psychotropic medications. Many newer, commonly prescribed psychotropic agents, including clozapine (Clozaril, FazaClo), olanzapine (Zyprexa), quetiapine (Seroquel), and risperidone (Risperdal), can cause significant weight gain, lipid abnormalities, and glucose dysregulation. Exercise may help such patients to modify their risk of these and other conditions. The research on the outcomes of exercise in people with serious mental illness has been limited, mainly consisting of case reports and small group studies. Reviews of these studies suggest that although exercise has little effect on the underlying mental illness, it may help to improve mood, decrease common symptoms such as lack of energy and psychosocial withdrawal, and relieve comorbid depression and anxiety. It also appears to improve brain and cognitive function in sedentary older adults, particularly when they're engaged in tasks involving executive functions,which are prominently impaired in schizophrenia. There are no known serious complications to the combination of exercise and psychotropic medication. In 2003 we conducted a pilot study with colleagues that was designed with two goals: to determine whether a regular walking program would specifically benefit people with serious mental illness and to test whether it could help them to exercise regularly.14 The study involved 15 outpatients with serious mental illness; diagnoses included schizophrenia or schizoaffective disorder (10 patients), bipolar illness (four patients), and major depression (one patient). The 12-week group walking program included educational workshops to increase motivation and provide support, and all walks were led by the principal investigator (one of the authors of this article, McDevitt) and a psychosocial case manager. Participants demonstrated high adherence both to walking (76% average attendance at the walking sessions) and to the 12-week program (87% completed the study). After the study ended, several participants formed a group in order to continue walking together.