Background: Evidence has accumulated that asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide (NO) synthase. Nitricoxide reduction is considered the hallmark of endothelial dysfunction. Objective: The study aimed to determine the value of the asymmetric dimethylarginine in patients with acute coronary syndrome as a predictor of major adverse cardiac events (MACE) and mortality during hospitalization and up to 6 months. Patients and Methods:  This study included 80 patients who were admitted to the critical care unit (CCU) with acute coronary syndrome. Serum ADMA marker was obtained within 24 hours of admission. Depending on ADMA value, patients were divided into three groups; Group A included patients with ADMA values up to 1.2 micromole/liter, Group B included those with ADMA values of more than 1.2 and up to 1.56 micromole/liter, and Group C comprised patients with ADMA value of more than 1.56 micromole/liter. During hospitalization and up to 6 months after discharge, patients were subjected to clinical follow-up to detect the occurrence of MACE including re-infarction, heart failure, re-intervention, and stroke or mortality. Results: Significant correlation was detected between ADMA value and patients' prognosis (i.e. as the ADMA value increased, the prognosis was worsened) with a significantcorrelation between patients' groups and prognosis with a P-value of 0.001. Conclusion: ADMA level had a prognostic value in patients with acute coronary syndrome with a cut-off value >1.2 micromole/liter, whereas patients with higher levels of ADMA were associated with a higher incidence of MACE and higher mortality than patients with lower levels of ADMA.