PurposeTo evaluate the safety and efficacy of radiotherapy combined with chemoimmunotherapy (RCIT) versus chemoimmunotherapy (CIT) alone as first-line treatment for oligometastatic esophageal squamous cell carcinoma (OESCC) at initial diagnosis.MethodsWe retrospectively evaluated 140 patients newly diagnosed with OESCC who received RCIT or CIT as first-line treatment between June 2018 and December 2021. Among them, 76 patients were in the RCIT cohort and 64 patients in the CIT cohort. Propensity score matching (PSM) was used to simulate random allocation.ResultsAfter 1:1 PSM, 61 well-paired patients were selected. The median follow-up duration was 34.7 months (95%CI: 30.6-38.8 months). After PSM, the median PFS for the RCIT and CIT groups was 10.9 (95%CI: 9.4-12.4) months and 7.3 (95%CI: 6.0-8.7) months, respectively (P = 0.004). The median OS for the RCIT and CIT groups was 22.4 (95%CI: 17.5-27.4) months and 13.4 (95%CI: 10.9-15.9) months, respectively (P = 0.031). There were significant differences in PFS (median PFS: 12.9 vs. 8.6 vs. 7.3 months, P = 0.003) between the group receiving radiotherapy (RT) for all lesions, the group receiving RT for partial lesions, and the CIT group, while OS was on the threshold of significance (median OS: 29.4 vs. 17.3 vs. 13.4 months, P = 0.052). No significant differences in the incidence of grade 3 or higher (G3+) treatment-related adverse events (TRAEs) were observed between the two groups. However, the incidence of G3+ pneumonitis (13.1% vs 1.6%, P = 0.038) were higher in the RCIT group compared to the CIT group.ConclusionRCIT as first-line treatment for OESCC was safe and efficacious. RCIT improved PFS/OS compared to CIT without increasing the overall high grade toxicity rate. However, the increased incidence of pneumonitis due to RT implementation cannot be disregarded.