A newborn infant with disseminated herpes simplex virus type 1 (HSV-1) infection was determined serologicallv to have acquired the infection postnatally; his mother was found to have HSV-1 in her breast milk but had no history of genital lesions and negative viral cultures of cervix, vagina, and throat. We suggest that HSV-infected maternal breast milk may be a source of this infection for susceptible infants.