BACKGROUND & AIMS: Platelet activation plays a major role in cardiovascular events (CVEs). Mediterranean diet (Med-Diet) reduces the incidence of stroke and myocardial infarction but it is still unclear if it affects platelet activation. Aim of the study was to evaluate the effect of Med-Diet on the urinary excretion of 11-dehydro-thromboxane (Tx) B2, a marker of in vivo platelet activation, in patients with atrial fibrillation (AF). METHODS: Prospective observational cohort study including 801 non-valvular AF patients on chronic treatment with warfarin/acenocumarol referring to I Medical Clinic - Atherothrombosis Center of Sapienza University of Rome, Italy, from February 2008 to December 2013. Adherence to Med-Diet was evaluated by a short nine-items dietary questionnaire. Urinary excretion of 11-dehydro-TxB2 was measured in all patients. RESULTS: Mean follow-up was 33.9 (±19.8) months, yielding 2223 patient/year of observation. Mean age of patients was 73.3 (±8.9) years, 43.7% were female. Median value of urinary TxB2 was 105.5 [60.0-190.0] ng/mg creatinine. We found a significant inverse correlation between total Med-Diet score and 11-dehydro-TxB2 values (Rs: -0.356, p