The SYNTAX score (SX score) is a useful score for assessing the severity of coronary artery disease (CAD). Previous studies have demonstrated a close relationship between SX score and inflammation. Procalcitonin (PCT) is an early inflammatory marker, especially during sepsis. Thus, in this study, we aimed to investigate the relationship between SX score and serum PCT levels. A total of 545 patients were enrolled in this prospective cross-sectional study and were divided into 2 subgroups, according to their SX score. Serum PCT and high-sensitivity C-reactive protein levels were measured. Serum PCT levels were higher in the high SX score group compared to the low-intermediate SX score group (P < .001). Serum PCT levels were an independent predictor of a high SX score in patients with acute coronary syndrome (P = .001). As patients with a higher SX score had increased serum PCT levels on admission, serum PCT may be useful for identifying patients with severe CAD.