Objective: Assessment of the effectiveness of an intervention aimed to increase adherence to the Mediterranean Diet (MeDiet). Design: 12-month assessment of a randomized primary prevention trial Subjects/settings: 1551 asymptomatic persons aged 55-80 years, with diabetes or 3 cardiovascular risk factors. Intervention: Participants were randomly assigned to a control group or 2 MeDiet groups. Those allocated to the 2 MeDiet groups received individual motivational interviews every 3 months to negotiate nutritional goals, and group educational sessions also on a quarterly basis. One MeDiet group received free virgin olive oil (1 L/wk), the other received free mixed nuts (30 g/d). Participants in the control group received verbal instructions and a leaflet recommending the National Cholesterol Education Program-III dietary guidelines. Main Outcome measures: changes in food and nutrient intake after 12-month. Statistical analyses: Paired t-tests (Within-group changes) and ANOVA (between-group changes). Results: Participants allocated to both MeDiets increased the intake of virgin olive oil, nuts, vegetables, legumes and fruits (P<0.05; all within- and between-group differences). Participants in the 3 groups decreased their intake of meat and pastries, cakes and sweets (P<0.05; all). Fiber, monounsaturated and polyunsaturated fatty acid intake increased in MeDiet groups (P<0.005; all). Favorable, although nonsignificant, changes in intake of other nutrients occurred only in the MeDiet groups. Conclusions: A 12-month behavioral intervention promoting the MeDiet can favorably modify the overall dietary pattern. Applications: The individual motivational interventions together with the group sessions and the free provision of high-fat and palatable key foods customary to the MeDiet, were effective in improving the dietary habits of participants in this trial.