A total of eighty one patients with resected stage II and IIIA non-small cell lung cancer treated with postoperative adjuvant radiation therapy between Jan. 1971 and Dec. 1990 were retrospectively analysed to evaluate whether postoperative radiation therapy improves survival. Patterns of failure and prognostic factors were also analysed. The 5 year overall and disease free survival rate were 40.5%, 43.4% and median survival 30 months. The 5 year actuarial survival rates by stage II and IIIA were 53.9% and 36.2%. Loco-regional failure rate was 14.7% and distant metastasis rate was 33.3% and both 4%. Statistically significant prognostic factor affecting survival was presence of mediastinal lymph node metastasis[N2]. This retrospective study suggests that postoperative radiation therapy in resected stage II and IIIA non-small cell lung cancer can reduce loco-regional recurrence and may improve survival rate as compared with other studies which were treated by surgery alone.