Neonatal herpes simplex virus infections can result in serious morbidity and mortality. Many of the infections result from asymptomatic cervical shedding of virus after a primary episode of genital HSV in the third trimester. Antibodies to HSV-2 have been detected in approximately 20 percent of pregnant women, but only 5 percent report a history of symptomatic infection. All primary episodes of HSV and secondary episodes near term or at the time of delivery should be treated with antiviral therapy. If active HSV infection is present at the time of delivery, cesarean section should be performed. Symptomatic and asymptomatic primary genital HSV infections are associated with preterm labor and low-birth-weight infants. The diagnosis of neonatal HSV can be difficult, but it should be suspected in any newborn with irritability, lethargy, fever or poor feeding at one week of age. Diagnosis is made by culturing the blood, cerebrospinal fluid, urine and fluid from eyes, nose and mucous membranes. All newborns suspected to have or who are diagnosed with HSV infection should be treated with parenteral acyclovir.