Background: Microalbuminuria is associated with adverse outcomes in acute coronary syndrome (ACS) patients.Methods: To evaluate the very long-term association between Microalbuminuria and the overall mortality and causes of death in this clinical setting, we prospectively studied 579 unselected ACS patients admitted to three hospitals. The baseline albumin-to-creatinine ratio (ACR) was measured on days 1, 3, and 7 in 24-h urine samples. Patients were followed for 22 years or until death.Results: Virtually all patients completed follow-up; 449(78%) had died: 41% due to non-sudden cardiac death (non-SCD), 19% sudden cardiac death (SCD), 40% due to non-cardiac (non-CD) death. Using unadjusted Cox regression analysis, ACR was a significant predictor of all-cause mortality (hazard ratio [HR] 1.26;95%confidence interval [CI] 1.22–1.31; p˂0.0001) and the three causes of death (HR 1.40;95%CI 1.32–1.48; p˂0.0001), (HR 1.22;95%CI 1.12–1.32; p˂0.0001) and (HR 1.16;95%CI 1.09–1.23; p˂0.0001) for non-SCD, SCD and non-CD respectively.Using a fully adjusted model, ACR was a significant independent predictor of all-cause mortality(HR 1.12; 95% CI 1.08–1.16; p˂0.0001) and only non-SCD (HR 1.21; 95%CI 1.14–1.29; p˂0.0001). There was a positive interaction between ACR level and history of AMI (HR 1.15; 95%CI 1.03– 1.29; p = 0.01) and the presence of heart failure at admission (HR 1.11; 95%CI 1.01–1.24; p =0.04), and negative interaction with higher than median LVEF (HR 0.89; 95%CI 0.80–0.99; p =0.03) for all-cause mortality at the multivariable level.Conclusion: Based on the present analysis, baseline urinary albumin excretion during ACS is a strong independent predictor of the very long-term mortality risk, chiefly due to non-sudden cardiac death.