Background: Radiation induced esophageal toxicity is a primary cause of treatment interruptions in the radiotherapy of lung cancer, for which there are no clear predictive factors. This study attempts to identify risk factors associated with the development of severe radiation induced esophageal toxicity using clinical and dosimetric parameters.Methods: We reviewed the medical records of 54 patients with histologically proven stage III non-small cell lung cancer treated with 3D-conformal radiotherapy at Alexandria Main University Hospital between January 2008 and December 2011. The original treatment plans for those patients were restored and imported to the treatment planning system. The external surface of esophagus was contoured for each patient. We calculated the esophagus dose–volume histograms and various dosimetric parameters. Univariate and multivariate logistic regression analyses were performed.Results: Of the 54 patients, 6 (11.1%) had grade 3 radiation induced esophageal toxicity and 2 (3.7%) had grade 4. There was no grade 5 toxicity. The most statistically significant parameters for predicting RIET grade 3 or worse included esophageal volume that received ≥50 Gy (V50), esophageal volume that received ≥55 Gy (V55), and the use of concurrent chemotherapy according to univariate and multivariate logistic regression analyses.Conclusion: This study demonstrates that the best predictive factors for severe early radiation induced esophageal toxicity are concurrent chemotherapy, and esophageal volumes ≥50 Gy and ≥55 Gy in non-small cell lung cancer treated with 3D-conformal radiotherapy.