The aim of the study was to compare the survival impact of concurrent versus sequential treatment with radiotherapy and chemotherapy in inoperable stage III non-small cell lung cancer (NSCLC). 85 patients were randomly assigned to one of the two treatment groups. In the sequential group, 45 patients had previously received sequential chemotherapy with 4 cycles of carboplatine and etoposide followed by conformal radiotherapy (RT). In the second concurrent group 40 patients received concomitant chemotherapy of cisplatine and etoposide and conformal RT followed by two cycles of consolidation chemotherapy of carboplatine and etoposide. We described all phases of the conformal three dimensional (3-D) RT. From November 2005 to October 2008, 93 patients were enrolled. Eight patients were not eligible, seven had stage IV and one had pleural effusion. All these were initially considered to have stage IIIB disease. The median survival was 13 months for the patients in the sequential group and 22 months in the concurrent treatment group. The difference was statistically significant (log-rank test p = 0.001). The disease-free survival was 9 months in the sequential group and 17 months in the concurrent treatment group. The difference was statistically significant (log-rank test p = 0.001) The 1- and 2-year survival rates were 73.6% and 39.7% in the concurrent group and 54.9% and 13.7% in the sequential group, respectively (log-rank test, p = 0.0011). Treatment-related toxicities were assessed according the RTOG/EORTC criteria. Acute esophagitis and incidence of neutropenia were higher with the concurrent than with the sequential treatment. Grade 3 esophagitis was characteristic only of concurrent treatment and it was a reason for radiotherapy interruption, but no longer than 7 days. Secondary anaemia was more frequent in the sequential treatment group. The statistical significant differences in survival suggest that concurrent chemotherapy and conformal three-dimensional radiotherapy is the optimal strategy for patients with locally advanced NSCLC.