Background: The purpose of this study was to determine the clinical and dosimetric factors associated with acute esophagitis (AE) in lung cancer patients treated with conformal radiotherapy (RT) in Turkey. Materials and Methods: In this retrospective review 104 lung cancer patients were examined. Esophagitis grades were verified weekly during treatment, and at 1 week, and 1 and 2 months afterwards. The clinical parameters included patient age, gender, tumor pathology, number of chemotherapy treatments before RT, concurrent chemotherapy, radiation dose, tumor response to RT, tumor localization, interruption of RT, weight loss, tumor and nodal stage and tumor volume. The following dosimetric parameters were analyzed for correlation of AE: The maximum ($D_{max}$) and mean ($D_{mean}$) doses delivered to the esophagus, the percentage of esophagus volume receiving ${geq}10$ Gy ($V_{10}$), ${geq}20$ Gy ($V_{20}$), ${geq}30$ Gy ($V_{30}$), ${geq}35$ Gy ($V_{35}$), ${geq}40$ Gy ($V_{40}$), ${geq}45$ Gy ($V_{45}$), ${geq}50$ Gy ($V_{50}$) and ${geq}60$ Gy ($V_{60}$). Results: Fifty-five patients (52.9%) developed AE. Maximum grades of AE were recorded: Grade 1 in 51 patients (49%), and Grade 2 in 4 patients (3.8%). Clinical factors had no statistically significant influence on the incidence of AE. In terms of dosimetric findings, correlation analyses demonstrated a significant association between AE and $D_{max}$ (>5117 cGy), $D_{mean}$ (>1487 cGy) and $V_{10-60}$ (percentage of volume receiving >10 to 60 Gy). The most significant relationship between RT and esophagitis were in $D_{max}$ (>5117 cGy) (p=0.002) and percentage of esophageal volume receiving >30 Gy ($V_{30}$ >31%) (p=0.008) in the logistic regression analysis. Conclusions: The maximum dose esophagus greater than 5117 cGy and approximately one third (31%) of the esophageal volume receiving >30 Gy was the most statistically significant predictive factor associated with esophagitis due to RT.