BACKGROUND Several factors and risk stratification tools have been studied to determine the prognosis of acute coronary syndrome. Fragmented QRS (fQRS) is a marker of myocardial scar and its prognostic role has recently been demonstrated. The present study aimed to investigate the association between the presence of fQRS in electrocardiogram and the prognosis of ST-segment elevation and non-ST-segment elevation myocardial infarction (STEMI and NSTEMI). METHODS A total of 661 patients with myocardial infarction (MI) were enrolled in a retrospective study. Based on the presence of fQRS in admission electrocardiogram, patients were divided into two groups. All patients were followed up for 6 months, and all major adverse cardiovascular events (MACE) were recorded. RESULTS The mean age of patients was 61.3 ± 1.2 years, and 71.7% were male. In the acute phase, the detection rates of regional wall motion abnormality and aortic valve insufficiency were higher in positive fQRS compared to negative fQRS group (p = 0.003). The incidence of total MACE was significantly higher in the positive fQRS compared to the negative fQRS group among all patients and in both STEMI and NSTEMI subgroups (p < 0.001). Based on multivariate analysis, the presence of fQRS and hypertension were the strongest predictors of total MACE at 6‑month follow-up (odds ratio [OR] = 5.929; 95% confidence interval [CI] = 3.620-9.709; p < 0.001 and OR = 2.220; 95% CI = 1.390-3.547; p < 0.001, respectively). CONCLUSIONS Regardless of the type of MI, it was found that the presence of fQRS on admission electrocardiogram can be implemented in risk stratification tools in patients with acute MI.