Comprehensive hospital discharge data completed by the California Office of Statewide Health Planning and Development was used to determine whether the proportion of infants </=6 weeks of age who were hospitalized with a diagnosis of herpes simplex virus (HSV) infection changed between 1985 and 1995. During 1985, 1990, and 1995, respectively, 11.7, 11.3, and 11.4 infants per 100,000 live births had a diagnosis of HSV (P=.98). The proportion of infants 1-42 days of age who were discharged from the hospital with a diagnosis of HSV infection did not change over this time period despite a decrease in deliveries by cesarean section and an increase in the proportion of women with a diagnosis of genital HSV infection who gave birth to infants by vaginal delivery. From 1985 to 1995 there was no decrease in the rate of secondary diagnosis of genital HSV in delivering women.