摘要BACKGROUND: We aim to investigate effects of metabolic syndrome on onset age and long-term outcomes in patients with acute coronary syndrome (ACS). METHODS: Patients with ACS (n=6,431) who underwent percutaneous coronary intervention from January to December 2013 were enrolled. After excluding patients with previous coronary artery disease, 1,558 patients were diagnosed with early-onset ACS (men aged ≤50 years; women aged ≤60 years) and 3,044 patients with late-onset ACS. Baseline characteristics and five-year clinical outcomes were measured. RESULTS: Body mass index, triglyceride, low-density lipoprotein cholesterol, and uric acid concentrations were significantly higher, while the high-density lipoprotein cholesterol (HDL-C) concentration was lower in the early-onset ACS group (P<0.001). Multivariate logistic regression revealed obesity (odds ratio [OR] 1.590, 95％ confidence interval [CI] 1.345-1.881), hypertriglyceridemia (OR 1.403, 95％ CI 1.185-1.660), and low HDL-C (OR 1.464, 95％ CI 1.231-1.742) as independent risk factors for early-onset ACS (all P<0.001). The five-year follow-up showed that the incidences of all cause death (1.5％ vs. 3.8％, P<0.001), cardiac death (1.1％ vs. 2.0％, P=0.023), and recurrent stroke (2.2％ vs. 4.2％, P<0.001) were lower, while bleeding events were more frequent in the early-onset ACS group. A subgroup analysis showed higher incidences of recurrent myocardial infarction (MI) and revascularization in patients with early-onset ACS and metabolic syndrome. CONCLUSIONS: Obesity, hypertriglyceridemia, and lower HDL-C level are independent risk factors for early-onset ACS, recurrent MI, and revascularization. The control of metabolic syndrome may reduce the incidence of early-onset ACS and improve the long-term prognosis.