In surgery for a parotid tumor, facial palsy is the most serious complication. Facial palsy tends to occur in the operation in which the facial nerve runs outside of the parotid tumor. Therefore, we developed the facial nerve electric stimulating test (FNEST) to determine more accurately the relationship between the facial nerve and the tumor. The FNEST diagnosed the condition in half of the patients whose facial nerve ran outside of the parotid tumor. Furthermore, a combination of CT and FNEST increased the diagnostic efficiency. The FNEST was a very efficient preoperative examination for estimating the course of the facial nerve.