In a prospective study still in progress, infants with congenital cytomegalovirus (CMV) infection were followed with audiological, ophthalmological, neurological, and psychological tests; 10,328 infants were investigated within a 5-year period (1977-1982) by virus isolation in urine within the first week of life. Fifty (0.5%) had a congenital CMV infection. In this group four children turned out to have total deafness and a fifth possibly a mild hearing disorder. In one case the deafness was associated with severe mental retardation and spastic tetraplegia. The mother of the child had a primary CMV infection in the first trimester. In one of the other cases of severe deafness it could be proven that the mother had had a secondary CMV infection and in further two cases, presumed secondary infections. Prospective serological tests of the mothers would not have revealed more than one of the high risk pregnancies. The value of vaccination against congenital CMV infection is questioned. Screening of newborn infants for congenital CMV infection is recommended in order to reveal infants at high risk for deafness and make an early habilitation possible.