INTRODUCTION: The promotion of Mediterranean Diets has generated some doubts, because of the concern that its high fat content might lead to the development of obesity. METHODS: Longitudinal analysis of 6319 participants in the SUN cohort study. We used a validated semiquantitative food frequency questionnaire (136 items). Baseline adherence to a Mediterranean dietary pattern (MDP) was assessed using a score (score_1) including vegetables, fruits, cereals, nuts, pulses, fish, olive oil and moderate consumption of red wine (positively weighted), whereas meat and dairy products were negatively weighted. We assessed the association between the overall baseline adherence to the MDP (score_1) and subsequent weight change after 28 months of follow-up. We also built another score (score_2) to assess changes in diet during follow-up and appraised the association between the joint exposure to both scores and weight change during follow-up. RESULTS: Participants in the first quartile of score_1 (lowest baseline adherence to MDP) showed a higher weight gain (+0.73 kg) than those in the top quartile (+0.45 kg). The results indicated an inverse dose-response relationship (P for trend = 0.016). A similar inverse association was apparent when we used change in adherence to the MDP (score_2). However, both inverse associations did not remain statistically significant after adjusting for relevant confounders. Consumption of dairy products was inversely associated with weight gain. CONCLUSIONS: Although participants increased their average weight during the follow-up period, weight increments were smaller among those with a higher adherence to an 'a priori' defined MDP. Results did not remain statistically significant after multivariate adjustment.