Radiotherapy plays an important role as a treatment for locally advanced non-small-cell lung cancer (NSCLC), but local failure still occurs in 70% to 80% of the patients. A retrospective analysis was carried out to evaluate the local control predictors for non-SCLC. From January 1990 to December 1996, 256 patients with stages I-IIIb NSCLC entered this analysis. All patients received definitive radiotherapy. The significance of prognostic variables on local control was evaluated using univariate analysis and Cox stepwise regression model. The prognostic index was calculated according to the value of each prognostic factor on local control. Median local progression-free survival time of the whole group was 9.7 months, and 1-, 3-, and 5-year actuarial local progression-free survival were 54%, 24%, and 19%, respectively. Univariate and multivariate analyses showed patients with smaller tumor volume, earlier clinical staging, and treated with higher total dose in shortened overall treatment time had better local control. Tumor volume, clinical staging, and radiotherapy methods were independent prognostic factors on local control. The prognostic index model could predict the local control condition of NSCLC treated with radiation therapy more effectively than a single variable such as TNM staging.