The proposed randomized trial investigates the effectiveness of lifestyle case management to encourage long-term lifestyle modifications in diet and physical activity, improve control of type 2 diabetes, reduce risk factors for progression of type 2 diabetes and cardiovascular disease, and improve quality of life, among health plan enrollees with type 2 diabetes and obesity. Patients agreeing to participate are randomly assigned to one of two conditions: 1) lifestyle case management, in which initial 12 month intensive diet and physical activity intervention is followed by 30 months of active maintenance directed by dietitians and physical trainers (the “lifestyle case management” group); 2) lifestyle intervention, in which there is no formal maintenance following the intensive lifestyle intervention (the “lifestyle intervention” group). Because the lifestyle case management intervention incorporates the content of the lifestyle intervention, we will be able to assess the incremental effectiveness of providing post-intervention lifestyle case management on glycemic control, cardiovascular risk, body composition, diet and physical activity habits, and health care utilization.