Background and aims: Smoking causes cardiovascular disease. AHRR hypomethylation at the cg05575921 site is associated with active and former smoking status at baseline, and cumulative amount of tobacco smoked. We tested the hypothesis that AHRR cg05575921 hypomethylation as an epigenetic marker of smoking history predicts the risk of myocardial infarction in former smokers. Methods: We included 10,510 individuals with methylation extent measurements and information on smoking status from the Copenhagen City Heart Study (CCHS), a prospective, cohort study of the general population carried out from 1991 to 2003. The endpoint myocardial infarction was retrieved from the national Danish Patient Registry and the national Danish Causes of Death Registry. Results: For individuals in the 1st (lowest) quartile of AHRR cg05575921 methylation (≤49% methylation extent), 99% were ever smokers at baseline (active and former smokers combined) compared to 42% in the 4th (highest) quartile (>62% methylation extent). For former smokers, the cumulative incidence of myocardial infarction was higher in the lowest methylation extent (1st-50th percentile) compared to the highest methylation extent (51st-100th percentile). Compared to never smokers, the multivariable adjusted subhazard ratio for myocardial infarction was 1.09 (95%CI:0.88–1.35) for former smokers with the highest methylation degree, 1.38 (1.06–1.80) for active smokers with the highest methylation extent, 1.39 (1.08–1.78) for former smokers with the lowest methylation extent, and 1.61 (1.35–1.92) for active smokers with the lowest methylation extent. Conclusions: AHRR cg05575921 hypomethylation as an epigenetic marker of smoking history predicts risk of myocardial infarction, particularly in former smokers. Further, AHRR hypomethylation, regardless of smoking status, was associated with increased risk of myocardial infarction.