Background: In this study, we aimed to analyze failure patterns, the clinical and biological prognostic factors for treatment outcomes, and evaluate the feasibility of involved-field irradiation (IFI) in patients with esophageal squamous cell carcinoma (ESCC) undergoing neoadjuvant chemoradiotherapy (CCRT). Methods: We retrospectively reviewed the medical records of 511 patients diagnosed with ESCC and underwent neoadjuvant CCRT and radical esophagectomy between January 2016 and February 2022 at Samsung Medical Center. For IFI, the clinical target volume (CTV) was defined as the primary gross tumor volume (GTV) plus a 2.0-3.0 cm longitudinal margin and a 0.5-1.0 cm circumferential margin, as well as the GTV of lymph nodes (LN) plus a 0.5-1.0 cm margin. For elective nodal irradiation (ENI), the CTV encompassed supraclavicular, mediastinal, or abdominal LN regions based on the primary tumor location. IFI was applied in most cases (98%). The failure patterns, loco-regional control (LRC), and survival outcome were analyzed. Regional lymph nodes (LNs) were defined and classified according to the AJCC 8th edition. Non-regional LNs were defined as metastatic LNs in neck, thorax, abdominal area except regional LNs. Results: With a median follow-up of 44.4 months, 213 (41.7%) patients experienced recurrence. The first recurrent sites were locoregional (LR) in 98 patients (19.2%), non-regional LN in 81 (15.9%), and distant organs in 152 (29.7%). Among the 98 patients with LR recurrence, RT in-field failure occurred in 53 (10.4%) patients, in & out-field failure in 18 (3.5%), and out-field failure in 27 (5.3%). In 27 cases of out-field failure only, LR recurrent lesion could be included in the target volume in 7 (1.4%) cases if ENIs were applied. Among the 27 patients, 10 received salvage treatment and 2 did not experience further recurrence. The analysis for the detailed LN recurrence showed that the upper mediastinal and supraclavicular LNs were the most frequent area, regardless of the primary tumor location and other clinical factors. Among 213 recurrent cases, 54 (10.5%) recurred in upper paratracheal LN and 40 (7.8%) in supraclavicular LN. The 5-year LRC rates, disease-control rates, and overall survival (OS) rates were 77.5%, 53%, and 54.3%, respectively. Multivariate analysis revealed that gender, age, cStage, ypStage, and resection margin status were independent prognostic factors for OS. Conclusions: Neoadjuvant CCRT using IFI with a small margin showed favorable treatment outcomes and out-field recurrence that the traditional ENI field could cover accounted for a small portion; thus, it might be feasible in the neoadjuvant setting. However, we need to consider that the upper mediastinal and supraclavicular areas were the most frequent recurrence sites.