||AIMS/HYPOTHESIS: Recent reviews indicate that the metabolic syndrome is a risk factor for cardiovascular disease and mortality, but evidence is scarce in elderly individuals. We therefore examined the relationship between the metabolic syndrome and mortality rates among individuals aged 40-59, 60-74 and 75-89 years. We also examined whether the syndrome was associated with mortality rates over and above the Framingham risk score. METHODS: We studied prospectively 6,748 men and women who participated in the Nord-Trøndelag Health Study, Norway, from 1995 to 1997 (HUNT 2) and defined the metabolic syndrome by the International Diabetes Federation criteria. RESULTS: During 53,617 person-years of follow-up (mean per person, 7.9 years), 955 individuals died, of whom 585 died from cardiovascular disease. Among individuals who were 40-59 years of age at baseline, the presence of the metabolic syndrome was associated with increased relative risk of cardiovascular and total mortality (age- and sex-adjusted hazard ratios 3.97 [95% CI: 2.00-7.88] and 2.06 [1.35-3.13], respectively, equivalent to population-attributable risks of 20.7 and 14.2%, respectively). The Framingham risk score accounted for less than one-third of the effect of metabolic syndrome on mortality rates. After the age of 60 years, the metabolic syndrome was not associated with increased mortality rates. We found a significant interaction between the metabolic syndrome and age on the relative risk of mortality. Results were confirmed in a sub-sample without cardiovascular disease at baseline. CONCLUSIONS/INTERPRETATION: The metabolic syndrome is a risk factor for mortality, over and above the Framingham risk score, in middle-aged, but not in elderly individuals.