OBJECTIVES: To examine patterns of health status, disability, and health-related quality of life in type 2 diabetes mellitus (T2DM) patients by comorbid obesity using a nationally representative US sample. METHODS: The 2009 Medical Expenditure Panel Survey was analyzed to identify adults (≥20 years) with diabetes (ICD-9-CM: 250). T2DM was identified if one of the following criteria was met: 1) evidence of ≥1 oral or non-insulin injectable anti-diabetic medication; 2) diagnosis of diabetes after age 30; 3) diagnosis before age 30 and not on insulin monotherapy. Self-perceived health status, limitation in activities of daily living (ADL)/instrumental ADL (IADL), and physical/mental component summary scores from the SF-12 were examined and compared by the presence of obesity (BMI≥30 kg/m2). Linear and logistic regressions were performed to assess the association between obesity and these outcomes. Nationally representative estimates were produced by applying population weights accounting for the multi-stage sampling design. RESULTS: This study included 2,269 respondents with T2DM (representing 19.2 million T2DM patients in the US), 54.5% of whom were obese. Compared to non-obese T2DM patients, obese diabetics had a higher proportion of self-perceived fair/poor health (41.9% vs. 34.5%, p<0.01) and limitations in IADL (12.1% vs. 8.7%, p=0.03), and a lower SF-12 physical score (38.4 vs. 42.3, p<0.01) while limitations in ADL and SF-12 mental score were similar. After adjusting for  age, gender, race, income, insured status, and comorbidities, obese T2DM patients were more likely to have limitations in IADL (OR=1.89, 95% CI:1.28-2.78) and scored 4.3 points lower on the SF-12 physical component (p<0.01) than non-obese patients, while no significant differences were found in reporting fair/poor health, limitations in ADL, and SF-12 mental score. CONCLUSIONS: T2DM patients with comorbid obesity had greater disability in IADL and worse physical health-related quality of life. The deleterious impact of obesity should be considered when managing T2DM patients.