The concept of natural orifice transluminal endoscopic surgery (NOTES) is an emerging experimental alternative to conventional surgery that eliminates skin incisions using an endoscope passed through a natural orifice (e.g., mouth, urethra, or anus). This study was designed to evaluate the feasibility and safety of thyroid resection via an entirely transoral tri-vestibular route using endoscopy, and to introduce NOTES to the head and neck area of medicine. We performed ten complete endoscopic thyroid lobectomies with central lymph node dissection via a tri-vestibular approach in fresh-frozen cadavers. A 5-mm endoscope with a deflectable tip was used to visualize the surgical field. Three cannulas were inserted through the midline and bilateral incision sites in the vestibule to position the instruments and endoscope. We refined and described the surgical technique in each step using video clips. We identified and preserved neighboring critical structures during surgery. We also confirmed that there were no obvious remnant thyroid tissues and no injury to the neighboring structures after exploration. The transoral tri-vestibular approach seems to provide a good view and surgical field for endoscopic thyroidectomy. However, the transoral approach for thyroidectomy remains experimental, and the detailed surgical technique should be refined via further clinical studies.