To assess the accuracy of self-reported data needed to constitute the metabolic syndrome in the University of Navarra Follow-Up [Seguimiento Universidad de Navarra (SUN)] cohort.The SUN project is a multi-purpose prospective cohort, formed by more than 20,000 university graduates, followed-up using surface mail questionnaires every 2 years. In a sample of 287 cohort participants, self-reported data on the criteria needed to define the metabolic syndrome (waist circumference, blood pressure, triglycerides, high-density lipoprotein-cholesterol and glucose) were compared with the same biometric data obtained by blood tests or measured by trained medical staff. Intra-class correlation coefficients with 95% confidence intervals (95% CI), relative mean error and agreement limits according to the method proposed by Bland and Altman were calculated for each variable studied.High intraclass correlations were found for the values of waist circumference (r=0.86, 95% CI: 0.80-0.90) and triglycerides (r=0.71, 95%CI: 0.61-0.79). Moderate intraclass correlations were found (between 0.46 and 0.63) for the other factors. Relative mean errors were always<2.5%, and >91% of values were within the limits of agreement for all variables.The results suggest that self-declared data on the criteria of metabolic syndrome obtained in the SUN cohort, though with some caution, are sufficiently accurate to be used in epidemiological studies.