Obesity is an escalating global health problem associated with both an increased risk of death and an increased risk of cardiovascular events. Our goal was to use magnetic resonance imaging (MRI) to determine the effect of obesity and weight loss, in the absence of the traditional cardiovascular risk factors, on aortic pulse wave velocity (PWV) a reliable, reproducible, and accurate clinical measure of aortic stiffness linked to increased mortality. Fifty obese (BMI 38.3 ± 6.8 kg/m(2)) and eighteen normal-weight controls (BMI 22.0 ± 1.7 kg/m(2)) with no identifiable cardiovascular risk factors underwent vascular MRI to assess PWV between the ascending aorta at the level of the pulmonary artery and the abdominal aorta (AA). Twenty-eight subjects underwent repeat imaging after a 1-year period of weight loss. Both groups were well matched for age, systolic blood pressure, fasting glucose, and total cholesterol. Obesity was associated with a 14% increase in PWV (P = 0.021), and with elevated C-reactive protein (CRP) (P < 0.01) and leptin levels (P < 0.001) factors known to cause increase arterial stiffness. Weight loss (average 50% excess weight) was associated with a 14% improvement in PWV (P = 0.03), and with reductions in serum leptin levels (P < 0.01). Obesity, in the absence of the traditional cardiovascular risk factors, is associated with increased aortic PWV, a noninvasive clinical measure of aortic stiffness independently predictive of cardiovascular mortality. Significant weight loss results in improvements in aortic PWV. This may provide a potential link between both obesity and increased mortality, and the reduction in mortality that occurs with weight loss.