Background and Objectives There is little data regarding the characteristics of young Vietnamese patients (<40 years old) who get acute coronary syndrome (ACS). This study aimed to compare the risk factors, clinical-subclinical characteristics, coronary lesions, and mortality prediction (based on the GRACE and TIMI scores) of young ACS patients with their older counterparts. Methods A cross-sectional descriptive study was conducted amongst 69 patients with ACS at the Cardiovascular Center of Hue Central Hospital from May 2017 to December 2018. These patients were divided into two groups: 33 patients were < 40 years old (group 1), and 36 patients were ≥ 40 years old (group 2). Demographic data, risk factors profile, clinical-subclinical characteristics, coronary lesions, and mortality prediction were compared between the two groups. Results Compared with group 2, group 1 had a higher proportion of severe angina (the prevalence of angina graded III-IV by CCS classification was 69.7% in group 1 versus 36.1% in group 2, P = 0.0108) and lower systolic pressure (median was 120 mmHg in group 1 versus 135 mmHg in group 2, P = 0.006). The prevalence of unstable angina and STEMI was higher in group 1 (51.5% and 36.4% in group 1 versus 30.6% and 11.1% in group 2, respectively), while NSTEMI was higher in group 2 (58.3% in group 2 versus 12.1% in group 1, P = 0.0002). The prevalence of single-vessel CAD, normal coronary angiography (CAG), nonobstructive CAD in group 1 was also higher and multi-vessel CAD was lower than group 2 (45.5%, 33.3%, 12.1% and 9.1% in group 1 versus 33.3%, 2.8%, 2.8% and 61.2% in group 2, respectively). The Gensini, GRACE, and TIMI scores were lower in group 1 (median was 5; medium was 78.55 and median was 2 in group 1 versus 37.5, 130.22 and 3 in group 2, respectively). Smoking was a risk factor for obstructive CAD in group 1 (OR = 7.12, 95% CI: 1.25–40.63, P < 0.05). Conclusion Young patients with ACS tended to be males, smokers, and with positive familial history; the grade of angina was more severe, and systolic pressure was lower; the prevalence of unstable angina and STEMI was higher. Smoking was a risk factor for obstructive CAD in young patients.