People with serious mental disorders tend to have shorter life expectancies and elevated rates of unhealthy behaviors and chronic illnesses. Peer-led medical illness self-management programs have been shown to be effective in improving the health and health behaviors of people with chronic medical conditions. This type of intervention, however, has yet to be systematically tested in individuals with mental disorders. Community mental health centers provide care to many people of low socioeconomic status who lack medical insurance. This study will evaluate the effectiveness of a medical illness self-management program in improving the health and health behaviors of people who are receiving care at a community mental health center.