To evaluate the prevalence of symptomatic versus asymptomatic or unrecognized type 2 herpes simplex virus (HSV-2) infection, the authors performed physical examination, viral cultures, and type-specific serologic assays in 776 randomly selected women attending an STD clinic and 636 female university students. Forty-six percent of women attending the STD clinic compared with 8.8% of the university students had serologic evidence of HSV-2 infection. Clinical or historical evidence of genital herpes was present in only 34% of the HSV-2 seropositive women attending the STD clinic and in 29% of the HSV-2 seropositive women attending the university clinic. Among women attending the STD clinic, the prevalence of recognized genital infection was more common among those with HSV-2 antibodies only versus those with HSV-1 and -2 antibodies (odds ratio = 2.39; 95% confidence interval = 1.30-4.37), suggesting that HSV-1 infection reduces the likelihood of recognizing HSV-2 infection. In view of the high proportion of seropositive individuals with unrecognized HSV-2 infection in both high and low prevalence HSV-2 seropositive populations, newly developed HSV type-specific serologic methods should be evaluated for detecting carriers of HSV-2 infection and counseling these individuals about strategies for avoiding sexual and perinatal transmission of HSV-2.