We investigated whether serotesting sexual partners of pregnant women for herpes simplex virus (HSV) improves adherence to safer-sex practices. A total of 287 HSV-2-seronegative pregnant women were recruited, and their partners were invited for HSV serologic testing. On the basis of test results, women were placed into 4 groups: those at risk for HSV-2 infection, those at risk for HSV-1 infection, those whose partner was not tested, and those not at risk for HSV infection. Women received safer-sex counseling and completed diaries of sexual activity. Women in HSV-2-serodiscordant couples (ie, those in relationships in which they were at risk for HSV-2 acquisition) reported a smaller percentage of days with unprotected genital sex acts as compared to women who were not at risk (2% vs 8%; relative risk [RR], 0.3 [95% confidence interval {CI}, .1-.8]; P = .002) and to women whose partners' HSV status was unknown (2% vs 11%; RR, 0.2 [95% CI, .1-.8]; P = .02). Women in HSV-1-serodiscordant couples showed no difference in the frequency of genital sex acts, unprotected genital sex acts, or oral sex acts as compared to those not at risk and to those whose partners' status was unknown. Pregnant women at known risk of HSV-2 acquisition by partner serotesting were less likely to engage in unprotected genital sex acts than HSV-2-seronegative women with partners who were negative or not tested.