Varicella-zoster virus (VZV) and herpes simplex virus (HSV) are considered to be the major causes of acute peripheral facial palsy (APFP). One hundred and forty-two patients with APFP were analyzed by serological assays and polymerase chain reaction analysis. Ramsay Hunt syndrome was diagnosed in 21 patients. Of the remaining 121 patients clinically diagnosed with Bell's palsy, VZV reactivation without zoster (zoster sine herpete) was detected in 35 patients (29%). The prevalence of antibodies to HSV among patients with Bell's palsy was significantly higher than the prevalence among those with VZV reactivation (Ramsay Hunt syndrome or zoster sine herpete). In contrast, a high incidence (88%) of VZV reactivation among HSV-seronegative patients with APFP was observed. Our data indicate that VZV is one of the major etiologic agents of clinically diagnosed Bell's palsy and that VZV reactivation causes APFP in most patients who lack antibodies to HSV.