Aims: To quantify the prevalence of coronary artery calcification (CAC) in relation to cardiovascular risk factors in marathon runners, and to study its role for myocardial damage and coronary events. Methods and results: In 108 apparently healthy male marathon runners aged ≥50 years, with ≥5 marathon competitions during the previous three years, the running history, Framingham risk score (FRS), CAC, and presence of myocardial late gadolinium enhancement (LGE) were measured. Control groups were matched by age (8:1) and FRS (2:1) from the Heinz Nixdorf Recall Study. The FRS in marathon runners was lower than in age-matched controls (7 vs. 11%, P < 0.0001). However, the CAC distribution was similar in marathon runners and age-matched controls (median CAC: 36 vs. 38, P = 0.36) and higher in marathon runners than in FRS-matched controls (median CAC: 36 vs. 12, P = 0.02). CAC percentile values and number of marathons independently predicted the presence of LGE (prevalence = 12%) (P = 0.02 for both). During follow-up after 21.3 ± 2.8 months, four runners with CAC ≥ 100 experienced coronary events. Event-free survival was inversely related to CAC burden (P = 0.018). Conclusion: Conventional cardiovascular risk stratification underestimates the CAC burden in presumably healthy marathon runners. As CAC burden and frequent marathon running seem to correlate with subclinical myocardial damage, an increased awareness of a potentially higher than anticipated coronary risk is warranted.