One hundred forty-seven women with recurrent symptomatic genital herpes simplex virus acquired prior to the start of pregnancy (group 1) and 15 women whose first symptomatic episode of genital herpes was acquired during pregnancy (group 2) were followed weekly during the course of gestation. Among women with recurrent genital herpes antedating pregnancy, the mean number of recurrences per trimester increased from 0.97 to 1.26 to 1.63 in the first through third trimester, respectively (p less than 0.05 for comparison between each trimester). The median number of symptomatic recurrences of genital herpes during gestation was four in women in group 1 compared to one in women in group 2 (p less than 0.01). Asymptomatic viral excretion from the genital tract was, however, more common in women in group 2 (33%) than in women in group 1 (12.9%) (p less than 0.05). Herpes simplex virus was isolated at 5.5% of routine visits in group 2 women compared to 1% of routine visits among group 1 women. Logistic regression analysis indicated young age also was associated with more frequent asymptomatic viral shedding. Asymptomatic herpes simplex virus excretion was more common from the vulvar area than the cervix, and women in group 2 were more likely to shed virus from both sites simultaneously than women in group 1. Age and recent acquisition of genital herpes are risk factors for asymptomatic excretion of herpes simplex virus during pregnancy.