Consolidative thoracic radiotherapy (cTRT) has been shown in phase III RCTs to improve overall (OS) and progression-free survival (PFS) after initial chemotherapy (chemo) in extensive-stage small cell lung cancer (ES-SCLC). This benefit was particularly pronounced in women compared to men in the 2015 CREST trial (hazard ratio [HR] 0.68 vs. 1.01, respectively). However, it is unknown whether similar findings would apply after chemoimmunotherapy (chemo-IO) became standard of care first-line treatment in 2018. In this analysis, we report national practice patterns and survival outcomes of cTRT versus no cTRT following chemo or chemo-IO, stratified by sex. Patients from the nationwide Flatiron Health de-identified electronic health record-derived database were included if they completed 4-6 cycles of first-line systemic therapy (platinum-doublet chemo or chemo-IO) for stage IV SCLC diagnosed between 2014 and 2021. Patients who progressed or started cTRT within 14 days or died within 90 days of completing systemic therapy were excluded to account for immortal time bias. We evaluated OS and PFS using multivariable Cox proportional hazards regression with receipt of cTRT as an independent covariate and last date of chemo as index date. As a sensitivity analysis to address potential selection bias, we weighted the models by the inverse probability of receiving cTRT. All OS and PFS analyses were stratified by systemic therapy type and sex. A total of 1,227 patients were included (850 chemo, 377 chemo-IO). The proportion of patients who received cTRT increased from 11.7% in 2014 to 20.7% in 2017, and then decreased to 16.4% in 2021. There were no statistically significant differences in baseline characteristics between patients who did and did not receive cTRT. In adjusted analyses among women receiving chemo, cTRT was associated with superior OS (HR 0.68; 95% confidence interval [CI] 0.51-0.91) and PFS (HR 0.64; 95% CI 0.47-0.86) [Table 1]. There was a non-statistically significant trend towards improved OS (HR 0.57; 95% CI 0.32-1.02) and PFS (HR 0.59; 95% CI 0.34-1.02) among women receiving chemo-IO. No OS or PFS benefit with cTRT was observed in men receiving either chemo or chemo-IO. Findings were similar in weighted analyses. The survival impact of cTRT may be differentially impacted by sex, with female patients appearing more likely to benefit than male patients regardless of systemic therapy type. While the underpinnings of this association need to be elucidated, stratification by sex should be considered for RCTs studying cTRT in ES-SCLC.