The purpose of the study was to reassess the utility of transforming growth factor-beta-1 (TGF-β1) together with dosimetric and tumor parameters as a predictor for radiation pneumonitis (RP). Of the 121 patients studied, 32 (26.4%) developed grade ≥ 1 RP, and 27 (22.3%) developed grade ≥ 2 RP. For the endpoint of grade ≥ 1 RP, those with V30 > 30% and an end-RT/baseline TGF-β1 ratio ≥ 1 had a significantly higher incidence of RP than did those with V30 > 30% and an end-RT/baseline TGF-β1 ratio < 1. For most other patient groups, there were no clear associations between TGF-β1 values and rates of RP. These findings suggest that TGF-β1 is generally not predictive for RP except for the group of patients with a high V30.