Background and Purpose: Lifestyle and diet affect cardiovascular risk, although there is currently no consensus about the best dietary model for the secondary prevention of cardiovascular disease. The CORDIOPREV study (Coronary Diet Intervention With Olive Oil and Cardiovascular Prevention) is an ongoing prospective, randomized, single-blind, controlled trial in 1002 coronary heart disease patients, whose primary objective is to compare the effect of 2 healthy dietary patterns (low-fat rich in complex carbohydrates versus Mediterranean diet rich in extra virgin olive oil) on the incidence of cardiovascular events. Here, we report the results of one secondary outcome of the CORDIOPREV study. Thus, to evaluate the efficacy of these diets in reducing cardiovascular disease risk. Intima-media thickness of both common carotid arteries (IMT-CC) was ultrasonically assessed bilaterally. IMT-CC is a validated surrogate for the status and future cardiovascular disease risk. Methods: From the total participants, 939 completed IMT-CC evaluation at baseline and were randomized to follow a Mediterranean diet (35% fat, 22% monounsaturated fatty acids, <50% carbohydrates) or a low-fat diet (28% fat, 12% monounsaturated fatty acids, >55% carbohydrates) with IMT-CC measurements at 5 and 7 years. We also analyzed the carotid plaque number and height. Results: The Mediterranean diet decreased IMT-CC at 5 years (−0.027±0.008 mm; P<0.001), maintained at 7 years (−0.031±0.008 mm; P<0.001), compared to baseline. The low-fat diet did not modify IMT-CC. IMT-CC and carotid plaquemax height were higher decreased after the Mediterranean diet, compared to the low-fat diet, throughout follow-up. Baseline IMT-CC had the strongest association with the changes in IMT-CC after the dietary intervention. Conclusions: Long-term consumption of a Mediterranean diet rich in extravirgin olive oil, if compared to a low-fat diet, was associated with decreased atherosclerosis progression, as shown by reduced IMT-CC and carotid plaque height. These findings reinforce the clinical benefits of the Mediterranean diet in the context of secondary cardiovascular prevention. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT00924937.