Background: Stellate ganglion block, which is one of the effective therapeutic tools for treating herpes zoster has been advocated by many investigators. However its efficacy is controversial at present. Objective: This study was conducted to examine the role of stellate ganglion block in the prevention of postherpetic neuralgia and relationships between the time of this treatment and the outbreak of postherpetic neuralgia. Methods: Twenty patients over the age of fifty with herpes zoster were included in this study. Before treatment, we randomly divided patients into two groups, A and B. Group A was treated with stellate ganglion block and acyclovir and group B was treated with acyclovir alone. Also we subdivided each group by starting treatment time into group 1 and 2. Group 1 was defined as the patients who began treatment within 2 weeks of the onset of the skin lesion. We observed the severity of pain and the incidence of postherpetic neuralgia according to each group. (continue...) (Korean J Dermatol 1999;37(5): 571-579)