Objectives: To evaluate the role of some parameters of dose volume hitograms (DVH) and plasma TGF-β levels in predicting radiation pneumonitis in non-small cell lung cancer (NSCLC) patients. Methods: Fifteen NSCLC patients treated with 3D conformal radiotherapy were included in the study. Radiotherapy dose was a median 60 Gy. Mean lung dose (MLD), V20 and V30 were calculated from both ipsilateral and contralateral lung DVH. TGF-β levels were studied with ELISA. Results: Median follow-up was 16 months (range 10-55). Radiation pneumonitis was diagnosed in three patients (6, 9, 12 months). Dose parameters of ipsi- and contralateral lungs revealed that higher MLD, V20, V30 values in contralateral lung were statistically significant for pneumonitis (p<0.005). There was no statistical correlation between plasma TGF-β levels and radiation pneumonitis. Conclusion: In this study, high doses in contralateral lung (MLD, V20, V30), when compared with ipsilateral lung, were shown as risk factors for developing radiation pneumonitis. TGF-β levels seem non-predictive for pneumonitis in the short term.