Introduction: Immature granulocytes (IG) in peripheral blood indicate increased bone marrow activation and inflammation, and SYNTAX score (SS) is an anatomical scoring system based on coronary angiogram. This study, aimed to evaluate the relationship between IG and SS, as a new inflammatory marker in patients with acute coronary syndrome (ACS). Methods: Patients aged >18 years who were diagnosed with ACS in the emergency department were included in this study, which was planned as a cross-sectional study. Patients were divided into two groups of patients with high and low SSs according to coronary angiography results. Demographic and laboratory parameters were compared between the groups. Results: Our study consisted of 78 patients diagnosed with ACS, who met the inclusion criteria. The average age of the study group was 59 years, and 67.9% of the patients were male. 21 patients (26.9%) had high SSs and 57 patients (73.1%) had low SSs. Mean IG% was significantly higher in high SS group compared to low SS group (0.71 +/- 0.25 vs 0.44 +/- 0.21 mg/dl, p<0.001). IG% can present a high SS with 76.2% sensitivity and 75.4% specificity at a cut-off value of 0.7. Conclusion: IG was significantly higher in ACS patients with high SSs. It seems that IG can be used as a parameter, which is quickly accessible and cheap, in order to predict high SS in ACS patients in daily clinical practice.