The authors examined whether obesity alone or as part of the metabolic syndrome (MS) increases coronary heart disease (CHD) risk in type 2 diabetes mellitus (T2DM) among 2970 adults aged 30-79 years in a French national sample. MS was defined as T2DM plus self-report of 2 or more of the following: body mass index >30 kg/m(2), diagnosed hypertension, or diagnosed dyslipidemia. A subsample with physician-reported data (n =841) was further classified with measured hypertension and dyslipidemia. Weight distribution included normal (21%), overweight (42%), and obese (37%). A 20% increased odds of CHD was estimated for every 5-kg/m(2) body mass index increase (P=.0001). MS was associated with a more than 2-fold higher risk of CHD compared with T2DM without MS (P<.0001, multivariate-adjusted [both samples]). With MS stratified by high-density lipoprotein cholesterol (<1.5 vs > or =1.5 mmol/L), compared with no MS, the odds ratio for CHD was 2.8 (normal-level high-density lipoprotein MS; 95% confidence interval, 1.8-4.5) and 1.5 (high-level high-density lipoprotein MS; 95% confidence interval, 0.8-2.9). The authors suggest that obesity alone and particularly when the MS is present--increases CHD risk in patients with T2DM. High levels of high-density lipoprotein may modify this relationship.