We examined prospectively the outcome of primary and nonprimary maternal cytomegalovirus (CMV) infection during pregnancy among 88 and 120 women, respectively. The risk for vertical transmission was 1.83x higher for primary infection than for nonprimary infection. Nonetheless, congenital CMV disease was diagnosed in both infection groups at similar rates. Cytomegalovirus (CMV) infection is the most frequent congenital infection and a common cause of deafness and intellectual impairment, affecting 0.5%-2.5% of all live births (1-3). Intrauterine infection occurs in 40% of primary maternal infections, with delivery of 10% to 15% symptomatic newborns and late neurologic sequelae in 10% of those asymptomatic at birth (1). Although preexisting maternal immunity reduces maternal-fetal transmission, the severity of congenital CMV disease is similar following primary or nonprimary infection (4-7). Yet, several reports found increased vertical transmission after nonprimary CMV infection (4-9). Therefore, our objective was to examine the outcome of primary and nonprimary maternal CMV infections during pregnancy.