To assess the long-term relationship between tree nut consumption and the risk of developing metabolic syndrome (MetS).Nut consumption was collected using a validated 136-item FFQ. The MetS was defined according to the International Diabetes Federation and American Heart Association/National Heart, Lung, and Blood Institute harmonizing definition. The association between nut consumption and MetS was assessed with logistic regression models adjusting for potential confounders. We compared the incidence of MetS between extreme categories of nut intake (> or = 2 servings/week v. never/almost never) after 6 years of follow-up.The SUN Project (Seguimiento Universidad de Navarra, University of Navarra Follow-up) is a prospective cohort study, formed of Spanish university graduates. Information is gathered by mailed questionnaires collected biennially. Nut consumption and MetS information was collected by self-reported data.Participants (n 9887) initially free of MetS or diabetes and followed up for a minimum of 6 years were included.We observed 567 new cases of MetS during follow-up. Participants who consumed nuts > or = 2 servings/week presented a 32% lower risk of developing MetS than those who never/almost never consumed (adjusted OR = 0.68, 95% CI 0.50, 0.92). The inverse association was stronger among participants who were health professionals.Nut consumption was significantly associated with lower risk of developing MetS after a 6-year follow-up period in a cohort of Spanish graduates.