Objective[|]In this study, we aimed to investigate the association of epicardial fat thickness (EFT) and coronary artery lesion complexity with patients having acute non-ST elevation myocardial infarction (NSTEMI).[¤]Materials and Methods[|]The patients (n=328) were divided into low syntax score (SS) group (SS≤17; Low-SSG), intermediate SS group (SS=18-28; In-SSG), and high SS group (SS≥29; High-SSG) based on the SS value. EFT, SS, distributions of the critical coronary artery lesions, and the neutrophil-lymphocyte ratio (NLR) were determined for all the groups. EFT was measured by transthoracic echocardiography and was recorded on a digital storage device.[¤]Results[|]High-SSG had a significantly higher mean of EFT (6.65±0.82 mm) when compared to Low-SSG (5.12±1.13 mm) and In-SSG (5.79±0.83 mm) (p<0.001). EFT showed a significant positive correlation with SS (r=0.607, p<0.001). Further, a significant positive correlation was revealed with the distributions of critical coronary artery lesions of the left anterior descending (LAD), circumflex artery (Cx), and right coronary artery (RCA) (r=0.260, p<0.001; r=0.213, p=0.001; and r=0.275, p<0.001, respectively). However, no correlation was demonstrated between EFT and NLR (r=0.081, p=0.145) in patients with NSTEMI.[¤]Conclusion[|]These results showed that EFT is significantly associated with coronary artery lesion complexity in patients with NSTEMI and can work as a risk marker in these patients.[¤]