Hypertriglyceridemia is a known cardiovascular risk factor. However, the relationship between serum triglyceride (TG) levels and the clinical outcomes in patients with acute myocardial infarction (AMI) is unclear. We conducted a single-center, retrospective observational study involving 538 consecutive patients with AMI who underwent emergent percutaneous coronary intervention within 12 hours of onset. Patients were categorized into three groups based on their serum TG levels at admission as follows: T1 group (TG <78 mg/dl, n=172), T2 group (78≤TG<141 mg/dl, n=177), and T3 group (141 mg/dl ≤TG, n=176). The primary endpoint was major adverse cardiovascular events (MACEs) defined as a composite of cardiovascular death, non-fatal MI, and non-fatal stroke. The median follow-up period was 2.4 (1.5-4.2) years. Patients in the T1 group were older, had a higher proportion of females, and had fewer cardiovascular risk factors. However, they also had a higher prevalence of multi-vessel coronary artery disease and severely calcified culprit lesions. The T1 group had a significantly higher rate of MACEs (20.4% in T1, 12.4% in T2 and 8.5% in T3, p<0.05 by Log-rank test, respectively). Multivariate analysis revealed that T1 was an independent predictor of MACEs (hazard ratio=2.19, 95% confidence interval=1.16-4.14, p<0.05). Although patients with AMI with low TG levels at admission had fewer coronary risk factors, they had more severe calcified culprit lesions and worse clinical outcomes.