The function of the facial nerve can be examined by four electrodiagnostic methods. In the nerve excitability test and electroneurography with determination of the distal latency the facial nerve is stimulated over the stylomastoid foramen. Chronaximetry and electromyography are performed in the muscles. Whereas chronaximetry renders an impression of the severity of neural lesion, electromyography can also determine the onset of reinnervation activity. Early prognosis within 6 days of onset can be determined only by nerve excitability test and electroneurography, preferred by us, which assesses the muscle potential. If the potential amplitude decreases more than 35% within two days and the muscle potential disappears between the fourth and sixth day, total degeneration of the nerve with poor prognosis is indicated. Such data can be gathered by at least two electrodiagnostic investigations preferably on the third day after onset and one to three days later. The cosmetic disfigurement through peripheral facial nerve palsy poses immediately the question of prognosis and of the therapeutic possibilities. Usually, this question can be answered by clinical examination alone. As soon as paralysis of facial muscles exists, prognostical statements can be made by electrodiagnostical methods alone. Because of the possiblility of operative treatment it is necessary to assess the infavorable courses early.