To assess health care resource utilization (HRU) and costs associated with comorbid obesity in patients with type 2 diabetes mellitus (T2DM) from 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. Pregnant women were excluded. Annual HRU and costs were compared for individuals with T2DM based on the presence of comorbid obesity (BMI≥30 kg/m 2 ). A generalized linear regression model adjusting for patient demographic and clinical characteristics was performed to assess the association between comorbid obesity and total health care costs. Population weights were applied to account for the multi-stage sampling design to produce nationally representative estimates. RESULTS: Of the 2,269 T2DM patients (representing 19.2 million individuals in the US), 54.5% were obese. Obese T2DM patients were more likely to be younger (59 vs. 65 years; p<0.01) than non-obese T2DM patients. Obese T2DM patients had similar inpatient hospital (17.8% vs. 17.9%; p=0.99) and emergency room (21.7% vs. 19.5%; p=0.33) utilization but utilized more outpatient hospital visits (33.3% vs. 27.9%; p=0.03), had more prescription medication fills (48.0 vs. 37.1, p<0.01) and higher total health care costs ($12,009 vs. $10,081, p=0.02) than non-obese T2DM patients. After controlling for age, gender, race, income, insured status and comorbidities, obese T2DM patients had total health care costs of 1.19 times those of the non-obese T2DM patients (p=0.04). CONCLUSIONS: Obesity appears to be associated with higher health care costs in T2DM patients. Effective weight management in T2DM patients may be costeffective and should be considered in diabetes treatment plans.