Background：Postherpetic neuralgia(PHN) is a distressing complication of herpes zoster that can persist for months or even years. Information on this condition is important because antiviral therapy may change the clinical course of the disease. Objective：The aim of this study is to estimate prevalence of PHN according to several risk factors. Methods：We observed prevalence of PHN in 96 patients who had herpes zoster with severe pain and treated with antiviral therapy during the admission. Also, we compared them by age group, dermatomal distribution, and starting day of antiviral therapy, respectively. Results：The prevalence of PHN according to the age was 5.9% in patients younger than 49 years, 40.0% in 50∼59 years, 46.9% in 60∼69 years, and 58.8% in 70 years and older. Sex and dermatomal distribution were not predictors of PHN. The odds ratio per one day difference in antiviral therapy was 1.62(95% confidence interval, 1.56 to 2.23). Conclusion：In herpes zoster with severe pain, age and starting day of antiviral therapy may be significant predictors of PHN. (Korean J Dermatol 2001;39(12)：1364~1369)