BACKGROUND: Although thoracic irradiation (TRT) is a standard treatment for elderly patients with locally advanced non-small-cell lung cancer (LA-NSCLC), treatment outcomes are poor. We previously reported a phase I trial combining S-1, an oral 5-fluorouracil derivative, and thoracic radiation, which yielded safe and effective outcomes. METHODS: In this phase II trial, 30 patients aged 76 years or older with LA-NSCLC received S-1 (80 mg/m(2) on days 1-14 and 29-42) and TRT (60Gy). The primary end-point was the response rate. RESULTS: The median age and pre-treatment Charlson score were 79 years and 1, respectively. The mean proportions of the actual doses of S-1 and TRT delivered relative to the planned doses were 95% and 98%, respectively. Partial responses were observed in 19 patients (63%; 95% confidence interval: 45-82%), which did not attain the end-point. At a median follow-up time of 23.7 months, the median progression-free survival and median survival times were 13.0 months and 27.9 months, respectively. No difference in efficacy was observed upon stratification by tumour histology. Toxicities were generally mild, except for grade 3 or greater febrile neutropenia and pneumonitis in 7% and 10% of patients, respectively. No patient developed severe oesophagitis. CONCLUSIONS: Although the primary end-point was not met, concurrent S-1 chemotherapy and radiotherapy yielded favourable survival data. Also, the combined treatment was well-tolerated in elderly patients with LA-NSCLC.