Glycated hemoglobin (HbA1c) is associated with an increased risk of cardiovascular disease and death from any cause. The aim of this study was to examine the relationship between HbA1c value and coronary artery lesion complexity. The subjects were 638 consecutive patients who underwent their first coronary angiography and had their HbA1c levels measured from December 2008 to August 2011. Sixty-one hemodialysis patients were excluded and 577 were analyzed. The complexity of the coronary artery lesions was evaluated using the SYNTAX score (SXscore). The subjects were divided into quartiles according to either the HbA1c or the fasting plasma glucose (FPG) values. Logistic regression analysis (with forced entry methods) was used to predict the prevalence of an intermediate or high SXscore. Both the higher HbA1c quartiles (Q1 to Q4) and higher FPG quartiles were significantly associated with a higher SXscore (p for trend <0.0001 and 0.026, respectively). The association between higher HbA1c quartiles and a higher SXscore was even observed in non-diabetic subjects (n= 433, Q1: 3.0±6.8, Q2: 6.9±15.6, Q3: 7.6±11.8, Q4: 7.4±13.4 p for trend= 0.004). In addition, a higher HbA1c quartile independently predicted patients with intermediate or high SXscores (SXscore ≥23) after adjusting for age, sex, hypertension, dyslipidemia, creatinine and FPG values (Odds ratio: Q1: 1.00 reference, Q2: 3.24, Q3: 3.03, Q4: 8.04). HbA1c is significantly associated with the complexity of coronary lesions. This association is even observed in non-diabetic adults. A higher HbA1c value is an independent predictor of the prevalence of complex coronary lesions.