Healthy People 2010 lists overweight and obesity as a Leading Health Indicator and estimates that over half of the adults in the United States are affected by this concern. People with serious mental illness are at a greater risk for obesity due to poverty, limited access to health care, poor health behaviors and the side effects of psychiatric medications. Obesity was targeted by this project due to: 1) the increased vulnerability of people with serious mental illness for becoming obese, 2) the relationship of obesity and other health conditions and 3) the paucity of successful weight loss interventions for people with serious mental illness (particularly in community-based settings). The proposed project examines the efficacy of a weight loss program for people with serious mental illness. The program innovation combines evidenced based weight reduction strategies with psychiatric rehabilitation theory and principles. The project is also innovative because it takes place in a community based setting. A randomized controlled trial will be conducted with 144 individuals with serious mental illness assigned to either the weight loss program or a treatment as usual control group. The intervention includes a 12 week intensive intervention followed by a 12 week maintenance program and six months of intermittent support. The intervention utilizes a combination of evidence based weight loss and psychiatric rehabilitation strategies. The intervention group meets once a week for three hours at a mental health community support program. The primary aim of this project is to examine the efficacy of the Psychiatric Rehabilitation Weight Loss program in reducing weight and body mass index (BMI). The secondary aims of this project include 1) examining the efficacy of a maintenance and support program in achieving long term weight loss 2) determining if medications with different weight gain profiles moderate the effects of the intervention, and 3) determining the efficacy of the Psychiatric Rehabilitation Weight Loss program in improving healthy lifestyle behaviors (nutrition and physical activity). Relevance - Obesity is a major threat to public health in the United States and is an even greater problem for people with serious mental. In examining the efficacy of a weight loss program for people with serious mental illness, this project has the potential to provide a model for addressing the public health issue of obesity in community-based mental health service settings.