The aim of this study was to assess if the entire mediastinum (M), the bilateral supraclavicular area (S), and the left gastric area (L) should be all included in the irradiation volume. The clinical data of 204 patients with thoracic esophageal squamous cell carcinoma who had undergone prophylactic postoperative radiotherapy after radical surgery were retrospectively reviewed. They were classified into four groups: group A, 26 patients with irradiated M alone; group B, 139 patients with irradiated M + S; group C, 10 patients with irradiated M + L; and group D, 29 patients with irradiated M + S + L. The 5-year disease-free survival rates were 36% in group A, 31% in group B, 40% in group C and 44% in group D (chi2=3.05, P =0.39), respectively. Multivariate analysis revealed that the irradiated extent was not a significant influential factor (hazard ratio=0.84, 95% confidence interval, 0.69-1.03, P =0.10). None of 43 patients without the L irradiated and with disease in the upper and middle upper thirds (defined in middle third but with upper third invaded), and one of 83 patients without the L irradiated and with disease in the middle third only thoracic esophagus were shown to have abdominal lymph node metastasis. Supraclavicular lymph node metastasis in patients in the lower and middle lower thirds (defined in middle third but with lower third invaded) were, respectively, 1/43 and 1/18 whether the S was irradiated or not. It seems unnecessary that the L be irradiated when the primary site is in the upper, middle, and middle upper thirds of the thoracic esophagus after radical surgery. Similarly, S may be unnecessarily irradiated in the lower and middle lower thirds.