Abstract Background/Introduction The Society for Cardiovascular Angiography and Interventions (SCAI) shock stage is useful for stratifying short-term prognosis in patients with acute coronary syndrome (ACS). However, the impact of culprit lesion location for ACS on prognostic stratification by the SCAI shock stage remains insufficiently elucidated. Purpose This study aims to investigate the association between culprit lesion location for ACS and shock severity on in-hospital mortality. Methods We retrospectively investigated consecutive ACS patients who underwent percutaneous coronary intervention at a single center between January 2014 and October 2023. Patients were classified into five groups (No risk, Stage A, Stage B, Stage C, and Stage E) based on data at arrival in the emergency department using SCAI classification. The following culprit lesions were included in this analysis: left main coronary artery (LMCA), proximal right coronary artery (RCA), proximal left anterior descending artery (LAD), and proximal left circumflex artery (LCX). Results Of 1,665 patients included in the analysis, the mean age was 72±12 years, and females accounted for 26% overall. The distribution of SCAI shock stages by culprit lesions is shown in Figure 1. The proportion of stage B or higher in the LMCA, RCA, LAD, and LCX was 41%, 23%, 24%, and 24%, respectively. The corresponding in-hospital mortality was 20%, 3%, 5%, and 3%, respectively. The trend of in-hospital mortality stratified by shock severity and culprit lesions is demonstrated in Figure 2. LMCA and LAD showed increased in-hospital mortality with progressing shock severity. In contrast, this trend was not observed for RCA and LCX. Conclusions Except for LMCA, the proportion of shock stage B or higher was comparable. SCAI shock stage classification was useful in stratifying in-hospital mortality in patients where culprit lesions for ACS were LMCA and proximal LAD. Conversely, its validity in those with proximal RCA and LCX may be limited.