The outcome of limited field irradiation for medically inoperable patients with peripheral stage I non-small cell lung cancer (NSCLC) was analyzed to discuss the elective irradiation of regional lymph nodes. From 1976 through 1994, 36 patients with peripheral stage I NSCLC were treated with definitive radiation therapy (RT) alone at Gunma University hospital. The total dose ranged from 60 to 81 Gy with a 2 Gy-daily standard fractionation, although only one patient received 48 Gy. Ten patients received elective irradiation of the regional lymph nodes with a total dose of 40 Gy or more. The overall response rate was 97% with 31% complete responses. The overall survival rates at 3 and 5 years were 42 and 23%, and disease-specific survival rates were 56 and 39% at 3 and 5 years, respectively. In 26 patients without the elective regional irradiation, disease-specific survival rates at 3 and 5 years were 53 and 40%, respectively, whereas they were 64 and 39% in 10 patients with the regional nodal irradiation. The cumulative 5-year local progression rate was 28%, and the overall progression rate was 60% at 5 years. Four patients had a local recurrence as the only site of initial tumor progression. Combined local and regional progression was seen in two patients, and one patient had a local recurrence in combination with distant metastasis. Twelve patients had distant failure without evidence of local or regional progression. Only one patient without regional nodal irradiation developed an isolated regional failure. No patient had serious complications related to RT. High-dose limited field RT is justified for medically inoperable patients with peripheral stage I NSCLC. The regional nodal irradiation can be omitted in these pulmonary compromised patients because of the low regional relapse rate. Dose-escalation by a conformal RT with a small target volume can be expected to provide a better local control rate and better survival.