The purpose of the study was to determine the relation between the incidence of radiation pneumonitis (RP) and available parameters from a dose-volume histogram (DVH) in patients with non-small cell lung cancer (NSCLC) who underwent three-dimensional conformal radiotherapy treatment. Between January 1999 and August 2003 in the Greatpoland Cancer Center, 62 patients with NSCLC were treated using three-dimensional conformal radiotherapy (3D CRT). All patients were treated 5 days per week with daily fractionation of 2 Gy to total dose of 60 Gy. All patients were available for analysis for symptomatic RP. Radiation pneumonitis was graded according to the RTOG/EORTC morbidity scoring classification. Logistic regression analysis was performed to test the association between RP and the following DVH parameters: mean lung dose (MLD), volume of lung receiving > or =20 Gy (V20 ) and > or =30 Gy (V30) and normal tissue complication probability (NTCP). Additionally, correlation of the following clinical factors such as: age, sex, tumor site, performance status (KPS), and additional therapy (chemotherapy) with incidence of the RP were performed. Moreover, correlation between DVH parameters were tested using Spearman method. Thirty out of 62 patients (48%) developed RP grade 0 or 1 (0 grade -- 12%, 1 grade -- 36%) and 32 (52%) grade 2 or 3 (2 grade -- 47%, 3 grade -- 5%). In the logistic regression analysis, all DVH parameters were associated with RP (p in range from 0.004 to 0.007). The strongest association was observed for NTCP and V30 (p=0.004). On the other hand, a weak association was found for V20 (p=0.007). The correlations between all DVH parameters for lung were sufficient (r Spearman in range from 0.87 to 0.93). The best correlation among DVH parameters were observed between V20 and NTCP (r=0.93, p<0.001). On the other hand, the least but sufficient association was found for V30 and V20 (r=0.87, p<0.001). There was no association between clinical factors and RP. NTCP and V30 parameters were the best predictors of symptomatic radiation pneumonitis for patients after three-dimensional conformal radiotherapy of non-small cell lung cancer.