The trigeminal function was investigated in 30 consecutive patients with acute unilateral peripheral facial palsy. The patients were tested with electrophysiological methods within 5 weeks after onset of the disease. Trigeminus-evoked potential test (TEP) disclosed trigeminal dysfunction in 47%, while the blink reflex test (BR) showed trigeminal pathology in 60% of the patients. A topographical analysis of the trigeminal system showed that 24% of the patients had BR patterns that were consistent with brainstem involvement. In 2 cases (7%), TEP was pathological though the BR test proved normal. These findings suggest a more central trigeminal affection and may demonstrate multifocal lesions. This was further underlined by the investigation of the auditory brainstem response (ABR) which indicated brainstem involvement in 28%. It is concluded that acute facial palsy is frequently a symptom of a central nervous affection.