Purpose We tested the feasibility and preliminary efficacy of a lifestyle intervention for middle-aged and older patients with schizophrenia and type-2 diabetes mellitus, using a randomized pre-test, post-test control group design. Method Individuals with a diagnosis of schizophrenia or schizoaffective disorder over the age of 40 were randomly assigned to 24-week Diabetes Awareness and Rehabilitation Training (DART; n =32) groups or Usual Care plus Information (UCI; n =32) comparison groups. Participants were recruited from board-and-care facilities and day treatment programs. Fifty-seven patients completed baseline and 6-month assessments consisting of an interview, measures of body mass index, blood pressure, fasting blood chemistry, and accelerometry. A mixed-model analysis of variance was used to analyze the data. Results A significant group×time interaction was found for body weight, with patients in the DART group losing a mean of 5 lb and those in the UCI gaining a mean 6 lb. Significant group×time interactions were also found for triglycerides, diabetes knowledge, diabetes self-efficacy, and self-reported physical activity, but not for fasting plasma glucose or glycosylated hemoglobin. Conclusions Group-based lifestyle interventions are feasible and produce positive health changes in middle-aged and older patients with schizophrenia and diabetes mellitus.