Background: Coronary artery disease (CAD) in adults <= 35 years of age is rare, but the incidence is on the rise and the risk factors for this age group are largely uncertain. Previous studies have shown that hyperurkemia (HUA) is an independent risk factor for CAD in the general population, whereas the role in adults <= 35 years of age with acute coronary syndrome (ACS) is unclear. Methods: Patients, 18-35 years of age, diagnosed with ACS for the first time at the documented institution between January 2005 and December 2015, were enrolled in the current study. The severity of CAD was assessed by the Gensini score. Patients were divided into two groups according to the definition of HUA. The relationship between HUA and CAD severity was assessed based on multi-variate analysis. Results: Seven hundred seventy-one participants fulfilling the criteria were included in this study (mean age, 31.6 years; 94.4% male). HUA, which was defined as a serum uric acid level >= 7.0 mg/dL (420 mu mol/L) in males and >= 6.0 mg/dL (357 mu mol/L) in females, accounted for 37% of the participants. Multivariate analysis identified that HUA is an independent risk factor of CAD severity, as assessed by the Gensini score, in very young adults with ACS (OR 8.28; 95% CI 1.96-14.59; p = 0.01), and the effect of HUA on CAD severity was second only to diabetes mellitus. Conclusions: Hyperuricemia was shown to be an independent risk factor for CAD severity in young adults with ACS (18-35 years of age).