Genital neonatal herpes simplex virus type 1 (HSV-1) infection was observed in a series of neonates after traditional Jewish ritual circumcision. The objective of this study was to describe neonate genital HSV-1 infection after ritual circumcision and investigate the association between genital HSV-1 after circumcision and the practice of the traditional circumcision. Eight neonates with genital HSV-1 infection after ritual circumcision were identified. The average interval from circumcision to clinical manifestations was 7.25 +/- 2.5 days. In all cases, the traditional circumciser (the mohel) had performed the ancient custom of orally suctioning the blood after cutting the foreskin (oral metzitzah), which is currently practiced by only a minority of mohels. Six infants received intravenous acyclovir therapy. Four infants had recurrent episodes of genital HSV infection, and 1 developed HSV encephalitis with neurologic sequelae. All four mohels tested for HSV antibodies were seropositive. Ritual Jewish circumcision that includes metzitzah with direct oral-genital contact carries a serious risk for transmission of HSV from mohels to neonates, which can be complicated by protracted or severe infection. Oral metzitzah after ritual circumcision may be hazardous to the neonate.