BACKGROUND: Few longitudinal studies have examined associations between body mass index (BMI) changes in adults with diabetes and the development of disability. OBJECTIVE: To investigate association patterns between BMI and disability in middle-aged adults with diabetes. DESIGN AND SETTING: Retrospective cohort design with data from the 1992-2006 Health and Retirement Study (HRS). A group-based joint trajectory method identified distinct BMI change trajectories and their link to subsequent disability trajectories. PARTICIPANTS: U.S. nationally representative adults aged 51-61 who reported a diagnosis of diabetes in the 1992 HRS (N=1,064). MEASUREMENTS: BMI and self-reported disability score were the main variables. Sociodemographic, clinical, behavioral, and diabetes-related factors were also examined. RESULTS: Four distinct weight trajectories (stable normal weight, 28.7 %; stable overweight, 46.2 %; loss and regain obese, 18.0 %; weight cumulating morbidly obese, 7.1 %) and three disability trajectories (little or low increase, 34.4 %; moderate increase, 45.4 %; chronic high increase, 20.2 %) best characterized the long-term patterns of BMI and disability change in middle-aged adults with diabetes. Adults in stable normal weight had the highest probability of being in the little/low increase disability group; however, one in five adults in that group progressed into chronic high disability, a higher proportion compared to the stable overweight group. CONCLUSIONS: Although there were various ways in which the two trajectories were linked, the beneficial impacts of optimizing weight in adults with diabetes were supported. In addition, the complexity of diabetes control in those with relatively normal weight was highlighted from this study.