Objective: The purpose of this study was to evaluate the clinical efficacy, histopathological efficacy, and response to preoperative thermochemoradiotherapy for N3 cervical lymph node metastases of oral cancer. Methods: Preoperative thermochemoradiotherapy was performed in 8 patients with oral cancer and N3 cervical lymph node metastasis. These patients underwent four-weekly sessions of hyperthermia, combined with radiotherapy (40 Gy) as well as chemotherapy with cisplatin (CDDP; 100 mg/m2), all prior to surgery. Radical neck dissection was performed 4 weeks after completion of preoperative thermochemoradiotherapy. Results: The preoperative treatment of cervical lymph node metastases yielded a partial response in 6 patients, while 2 patients demonstrated no change. Histopathologically, grade III was detected in 1, grade IIb in 4 and grade IIa in 3 patients after surgery, according to the criteria of Shimosato. The follow-up period ranged from 13 to 64 months (mean 34). Of the 8 patients, 2 died (1 of lymph node metastasis and 1 had metastasis to a distant site), and 6 patients were alive at the last follow-up, with the longest postoperative disease-free survival being 63 months. The 5-year cumulative survival rate was 70.0%. Conclusion: These results indicate that preoperative thermochemoradiotherapy is a promising modality for patients with N3 cervical lymph node metastasis of oral cancer.