Aims Guidelines do not differentiate between the available assays of cardiac troponin (cTn). We compared the prognostic and predictive ability of cTn assays. Methods and results This was a nationwide cohort study of patients with acute coronary syndrome (ACS) and >= 2 cTn measurements of one of four assays: Roche high-sensitivity cTnT (hs-cTnT), Abbott high sensitivity cTnI (hs-cTnI), Siemens Vista cTnI, and Siemens cTnI Ultra. Data were collected from Danish registries from 2009-18. Peak cTn concentration normalized to the 99(th) percentile was used. Outcomes were myocardial infarction (MI) during admission, one-year all-cause-, cardiovascular-, and non-cardiovascular mortality. Receiver operating characteristics and logistic regression calculating odds ratios (OR) were used. A total of 90 705 patients were included, of which 20 550 (23%) had MI. Siemens Vista cTnI was the strongest predictor of MI, Area under the curve (auc) 0.93 (95% CI 0.93-0.93). In 1 year 9012 (9.9%) of patients had died. An inverted U-shape relationship was observed between concentration of cTn and all-cause mortality. Hs-cTnT OR 21.3 (95% CI 18.4-24.8) at 2-5 times the 99(th) percentile and 12.1 (95% CI 10.3-14.1) for concentrations >100 times the 99(th) percentile. The inverted U-shape relationship was only present for non-cardiovascular mortality. The strongest predictor of cardiovascular mortality was hs-cTnT, OR 11.3 (95% CI 6.4-21.8) at 1-2 times the 99(th) percentile and 88.8 (95% CI 53.2-163.0) for concentrations >100 times the 99(th) percentile. Conclusion Siemens Vista cTnI was the strongest predictor of MI and hs-cTnT was the strongest predictor of mortality. An inverted U-shape relationship was observed between cTn concentration and non-cardiovascular mortality.