Overweight and obesity are highly prevalent among persons with severe mental illness (SMI); these conditions likely contribute substantially to premature cardiovascular disease and the 20 percent shortened life expectancy in SMI. Persons with SMI need effective, appropriately tailored behavioral interventions to achieve and maintain weight loss. Psychiatric rehabilitation programs provide logical intervention settings because consumers often attend regularly and exercise can take place on-site. Through the NIMH R34,"Achieving Healthy Lifestyles in Psych Rehabilitation", we tailored a comprehensive behavioral weight loss intervention efficacious in the general population to persons with SMI in psychiatric rehabilitation centers. We performed a pre/post pilot study (n=52) and demonstrated preliminary efficacy with high levels of recruitment, retention and demonstrated weight loss. The objective of this R-01 application is to perform a randomized clinical trial (ACHIEVE Trial) to definitively test the efficacy of this innovative, practical intervention to accomplish and sustain weight loss in overweight and obese persons with SMI. In the proposed multi-site trial, we will enroll 320 consumers with SMI who attend ten psychiatric rehabilitation centers in urban and suburban areas across Maryland and randomize participants to the ACHIEVE intervention or usual care. Intervention participants will receive group and individual weight management education and counseling sessions and group physical activity classes at each site. In the initial 6 month intensive intervention period, study interventionists will lead the sessions and also train rehabilitation program staff. A 12 month maintenance intervention will follow where interventionists continue leading some sessions and rehabilitation staff gradually assume responsibility for delivering much of the intervention. Co-primary outcomes will be change in weight from baseline to 6 and 18 months. Secondary outcomes will be change at 6 and 18 months for: a) moderate physical activity by accelerometry and physical fitness by 6 minute walk; b) waist circumference; c) lipids; d) blood pressure; e) Framingham cardiovascular risk score; f) health status with SF-36; and g) depression symptoms with CES-D. We also will evaluate formally intervention cost. This proposed multi-site randomized clinical trial will provide a rigorous evaluation of a practical behavioral intervention designed to accomplish and sustain weight loss in persons with SMI. If successful, the intervention will be a model program that could be disseminated widely and should provide important health benefits by ameliorating cardiovascular disease risk in this vulnerable population. Obesity is very common in persons with severe mental illness, and effective weight-loss interventions for this high-risk group are needed urgently. We will perform a randomized trial in 10 psychiatric rehabilitation centers to test a practical weight-loss intervention with nutrition counseling and exercise classes that is proven in the general population and tailored to persons with severe mental illness. If successful, the intervention will be a model program that could be disseminated widely and should provide important health benefits by decreasing heart disease risk in this vulnerable population.