PURPOSE: To evaluate effect of postoperative radiotherapy on survival and local control for patients with non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: Ninety two NSCLC patients with N1or N2 involvement who were treated with postoperative radiotherapy following surgery with curative intent from May 1987 to October 1999 were retrospectively analyzed. Age of the patients was ranged from 32 to 78 years. According to TNM Stage, 35 patients had Stage II and 57 had Stage III disease. There were 49 patients with N1 involvement and 43 patients with N2 involvement. Fifty six patients were noted to have T1~2 tumors and 36 patients to have T3~4 tumors. Delivered total dose was ranged from 40 to 60 Gy. Majority of patients received 50 Gy or 50.4 Gy. Follow-up period was ranged from 9 month to 7 years with median follow-up of 26 months. RESULTS: Overall survival rates at 3 and 5 years for entire group of patients were 46% and 38%, respectively. Corresponding disease free survival rates were 44% and 36%. There was significant difference in survival between patients with Stage II and Stage III disease (50% vs 28% at 5-year). Five year survival rates for N1 and N2 patients were 52% and 20%, respectively (p<0.05). These were 40% and 34% for patients with T1~2 tumors and T3~4 tumors. There were documented local relapses in 13% of the patients. For patients with N1 and N2 Stage, local relapse rates were 8% and 18%, respectively. CONCLUSION: Our study confirms that postoperative radiotherapy for patients with non-small cell lung cancer improves local control. However, influence of postoperative radiotherapy on long-term survival is less clear. More effective systemic treatment to prevent distant metastasis should be investigated in future study to improve long-term survival.