The purpose of this study was to determine seroprevalence of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in a national cross-sectional sample of pregnant women.Pregnancy tests (urine and serum) were performed for female patients 12-59 years of age who participated in the National Health and Nutrition Examination Survey from 1999-2002. Immunodot assays were used to detect antibodies to HSV-1 and HSV-2.The mean age of the 626 pregnant women was 27 years, and the median number of lifetime sex partners was 4. Overall, HSV-1 seroprevalence was 63%; HSV-2 seroprevalence was 22%; infection with both HSV-1 and HSV-2 was 13%, and HSV seronegativity was 28%. HSV seroprevalence differed by race/ethnicity, with nonHispanic white patients more likely to be seronegative compared with other racial/ethnic groups (40% vs 11%; P.001). The number of lifetime sex partners was also associated with serostatus. On the basis of serostatus-specific rates of neonatal herpes from a published study, the rate of neonatal herpes is projected to be 33/100,000 live births and is 40% higher in nonHispanic white women than in other racial/ethnic groups.The seroprevalence of HSV-1 and HSV-2 varied by race/ethnicity; babies born to nonHispanic white mothers, whose HSV seroprevalence was the lowest, appear to be at greater risk for neonatal herpes.