Radiotherapy (RT) is widely used in the management of lung cancer but age-oriented randomized trials are lacking in older-unfit patients. We started a prospective study to evaluate the toxicity and efficacy of definitive RT in very old-unfit patients with non-small cell lung cancer (NSCLC) in clinical stage IIIA, according to AJCC 1988. Forty patients, age > or = 75 years, Karnofsky Performance status (KPS) > or = 60, unfit to receive an aggressive combined treatment, were entered in the study. Each patient had one or more comorbidities, and the Charlson score was greater than two in 7/40. All patients were treated with radiation fields encompassing the primary tumor and grossly involved lymph nodes. A median radiation dose of 60 Gy/2 Gy day/5 days a week, was delivered. The 40 patients have been followed up, including those who died, for a potential median time of 4.6 years. As results, no treatment-related mortality, and clinically insignificant acute morbidity was recorded: in 28/40 cases a mild esophagitis occurred. Two patients showed a clinical radiation pneumonitis (RP). Late normal tissue damage was represented by lung fibrosis (40/40 patients). The treatment was efficacy since each patient obtained some clinical benefit from it. Median survival (MS) was 19 months (range 5-68); the 3 and 5-year actuarial survival was 18 and 12%, respectively. In conclusion, we think that older patients with concomitant illness can be submitted to curative 'involved field' irradiation and the results observed in this trial encourage to use curative RT in older subjects with local-regionally advanced NSCLC and co-morbid condition.