The aim of this study was to evaluate the prognostic value of interleukin-6 (IL-6) for myocardial infarction (MI) and mortality in a population with stable coronary artery disease (CAD) during a mean period of 6.3 years. IL-6 is a major proinflammatory cytokine of acute phase response; elevated levels are associated with worse prognosis in unstable angina and after acute MI. However, data regarding its long-term prognostic value in stable CAD are limited and controversial. A nested case-control study design was used. Of 3,090 patients with stable CAD, 129 with an adequate blood sample for IL-6 and who reached the end points (MI or sudden death) were randomly selected. Each case was 1:1 matched with 129 controls (alive at the end of the study and free of cardiovascular events) according to age, gender, and treatment. Of the 129 cases, 113 had a MI as the initial event, and for the other 16 the initial event was sudden death. There were 8 patients who first had a MI and later died suddenly. IL-6 was significantly higher in cases (2.34 pg/ml) than in controls (1.65 pg/ml) (p = 0.0004). IL-6 was significantly correlated with C-reactive protein (r = 0.2, p = 0.002); a borderline significance was also found for fibrinogen (r = 0.11, p = 0.07). Each increase of 1 pg/ml in IL-6 was associated with a 1.70 (range 1.23 to 2.45) increased relative odds of subsequent MI or sudden death. Events rate per 1,000 patients-years for the 5 quintiles of IL-6 were 72.26, 89.61, 79.76, 142.53, and 181.08, respectively (p <0.0001). A significantly higher risk in the upper quintile was found (odds ratio, 3.44; 95% confidence interval 1.57 to 8.13). In conclusion, elevated IL-6 levels are strongly associated with future cardiac events and mortality in a population with stable CAD during a long-term follow-up.