New serological methods, based on the detection of type-specific antibodies to herpes simplex virus (HSV) glycoproteins, have allowed a reappraisal of the prevalence of genital herpes. During the 1980s, genital herpes continued to be an infection of epidemic proportions in many developed countries. In the USA, although there was evidence of a decline in the age-specific prevalence of HSV type 1 (HSV-1) infection, the seroprevalence of HSV type 2 (HSV-2) has continued to increase. Among those attending sexually transmitted disease clinics in the USA, 30-50% of adults now have antibodies to HSV-2. Only a minority of HSV-2 infected persons present with clinical disease related to this infection. In some countries, an increase in the incidence of severe primary genital infections caused by HSV-1, which often occur in monogamous relationships, has been reported. Genital ulcer disease, of which genital herpes is the most common cause in developed countries, is an important risk factor for the acquisition and transmission of human immunodeficiency virus (HIV) infection. Furthermore, evidence is accruing for a potential role of HSV reactivation in the progression of immune deficiency in HIV-infected individuals.