Abstract: Small cell lung cancer (SCLC) is a neuroendocrine tumor that is highly heterogeneous and invasive. SCLC is prone to distant metastasis, and most patients are diagnosed in the extensive stage (ES-SCLC) after metastasis has occurred. Immune checkpoint inhibitors (ICIs) combined with chemotherapy currently serve as standard first-line treatment for ES-SCLC. However, the accompanying immune-related adverse events (irAEs) may affect patients' quality of life and treatment efficacy. Studies suggest a correlation between irAE occurrence and treatment response rates as well as survival benefits, although the mechanisms underlying this correlation are not fully understood. This article provides a comprehensive review of the application of ICIs in ES-SCLC, exploring the association between irAEs and clinical ICI efficacy, the potential underlying biological mechanisms of their association, predictive biomarkers of irAEs, and strategies for managing irAEs. This study offers insights for optimizing immunotherapy for treating ES-SCLC.