<p>To compare response evaluation criteria using RECIST 1.1, iRECIST, and imRECIST in non-small cell lung cancer (NSCLC) patients treated with PD-1/PD-L1 immune checkpoint inhibitors (ICI) and investigate their discrepancy and impact on survival. This retrospective cohort study included 105 NSCLC patients treated with PD-1/PD-L1 across four hospitals. Response assessments were conducted using RECIST 1.1, iRECIST, and imRECIST criteria after viewing relevant images before and after ICI treatment. The absolute and relative differences on time point (TP) assessments and best overall response (BOR) categories regarding progressive disease (PD) across criteria were reported. The Kaplan-Meier analysis and log-rank test were used to evaluate the differences of overall survival (OS) between concordant or discordant assessments among criteria. Discordant TP assessments were observed in 25 patients (23.8%) across the three criteria. Among them, 15.2% were labeled as PD by RECIST 1.1 and iRECIST but not by imRECIST. Comparing imRECIST with RECIST 1.1, 10 patients (9.9%) had discordant BOR for PD (classified as non-PD by imRECIST but PD by RECIST 1.1). These patients had a median OS of 8.1 months, falling between the concordant disease progression group (2.8 months) and the concordant disease control group (26.8 months) (<i>p</i> &lt; 0.001). In contrast, only 2 patients (1.9%) had discordant BOR for PD between iRECIST and RECIST 1.1. The imRECIST identified 9.9% of NSCLC patients who may potentially benefit from continuing ICI treatment despite a classification of PD with RECIST 1.1. The discordance between iRECIST and RECIST 1.1 was relatively smaller.</p>