Objective: The aim of this trial was to determine whether obese patients benefit from treatment with rimonabant in terms of progression of carotid atherosclerosis. Rimonabant, a selective cannabinoid-1 receptor blocker, reduces body weight and improves cardiometabolic risk factors in patients who are obese. Design, setting, patients, interventions and results: A prospective, double-blind, placebo-controlled trial (Atherosclerosis Underlying Development assessed by Intima - media Thickness in patients On Rimonabant (AUDITOR)) randomised 661 patients with abdominal obesity and metabolic syndrome to rimonabant or placebo for 30 months of treatment. The absolute change in the average value for six segments of far wall carotid intima - media thickness from baseline to month 30 was 0.010±0.095 mm in the rimonabant group and 0.012±0.091 mm in the placebo group (p=0.67). The annualised change was an increase of 0.005±0.042 mm for the rimonabant-treated group and 0.007±0.043 mm for the placebo-treated group (p=0.45). Conclusions: There was no difference in atherosclerosis progression between patients receiving rimonabant for 30 months and those receiving placebo for the primary efficacy measure (absolute change in carotid intima - media thickness). These findings are consistent with a similar study using coronary intravascular ultrasound and another study evaluating the occurrence of cardiovascular events. Our findings suggest that a 5% loss of body weight over a 30-month period with rimonabant is insufficient to modify atherosclerosis progression in the carotid artery in obese patients with metabolic syndrome. Clinical trial registration information: clinicaltrials.gov Identifier: NCT00228176.