March 1988 through April 1992, three hundred and ninety-six patients affected with bronchogenic carcinoma were treated at the Department of Radiation Oncology of the S. Anna Hospital, Como, Italy. A hundred and ten patients presenting stage-III non-small-cell lung carcinoma were evaluable. All evaluable patients underwent radiation therapy alone, with either palliative or curative purposes. Two main periods can be distinguished: in period A, before June 30th, 1990, treatment planning included conventional techniques, with no simulators; the patients were treated with opposing anteroposterior fields only. In period B, after July 1st, 1990, either the simulator alone was used or a simulator, a CT unit and a treatment planning computer system were combined; anteroposterior opposing fields or multiportal technique were used. Median overall survival was 10 months. Independent of treatment goals, the irradiated volume was markedly different in the patients treated in period A than in those treated in period B. A marked and statistically significant increase in survival was observed in group B. Survival also increased in patients treated with doses > 40 Gy, but only if treatment planning had used adequate technology and accuracy. To conclude, better survival can be achieved only by improving treatment accuracy and quality.