Aortic stiffness is predictive of cardiovascular diseases (CVD) and mortality in lifestyle-related diseases. The cardio-ankle vascular index (CAVI), a new index of arterial stiffness, was recently developed by measuring of pulse wave velocity (PWV) and blood pressure (BP). CAVI is adjusted for BP based on stiffness parameter beta and is less influenced by BP, suggesting its superiority over brachial-ankle PWV (baPWV). However, there are currently no reports on the usefulness of CAVI as an atherogenic index in obesity and metabolic syndrome (MS). Among the 325 obese Japanese outpatients enrolled in the multi-centered Japan Obesity and Metabolic Syndrome Study, 216 patients (67%) met the criteria of MS according to the modified National Cholesterol Education Program-Adult Treatment Panel III. CAVI values were significantly higher in MS than in non-MS patients, whereas there was no significant difference in body mass index, total cholesterol, and low-density lipoprotein-cholesterol between both groups. CAVI values were weakly correlated with BP but closely correlated with the severity of MS and MS-related parameters such as hypoadiponectinemia, relative to baPWV. Furthermore, weight-reduction therapy through diet and exercise over a 3-month period significantly decreased CAVI values in parallel with increasing adiponectin. This study demonstrates for the first time that CAVI is a good indicator of arterial stiffness. It is closely correlated with the severity of MS and CVD risks in obesity and independent of BP, and is thus superior to baPWV. Therefore, the determination of arterial stiffness by CAVI may be useful for evaluating and managing the CVD risks of MS patients.