PURPOSE: The aim of this study is to look for the possible efficacy of external irradiation for locally advanced papillary thyroid cancers (stage pT4 or N1). METHODS AND MATERIALS: From August 1981 through September 1997, 91 Patients with locally advanced papillary thyroid cancers (stage pT4 or N1) have been treated with external irradiation and followed up at our clinic. All of the patients have been treated with surgical resection. After surgery, 23 patients received postoperative external irradiation with or without ablative radioiodine therapy, whereas the other 68 patients were treated with ablative radioiodine therapy alone. Distributions of sex, age, and stage were comparable in both irradiated and nonirradiated groups. Multivariate analysis of the influence by age, sex, stage, ablative radioiodine therapy and external irradiation on local control were performed by using Cox's proportional hazard model. RESULTS: Overall survival rates at 7 years were of no significant difference in both groups. There were 98.1% for no RT group and 90% for RT group (p=0.506).5-year local control rates were significantly different, these were 95.2% for RT group and 67.5% for no RT group (p=0.0408). An analysis of the prognostic factors, age, sex, stage, and RAI were not significant variables, except for the external irradiation. CONCLUSION: Adjuvant postoperative external irradiation did not affect overall survival, but significantly improved local control in the patients with locally advanced papillary thyroid cancers (stage pT4 or lymph node involvement).