A prospective study of congenital cytomegalovirus infection in Malmö, Sweden, was performed from 1977 through 1985. The diagnosis was based on isolation of cytomegalovirus soon after birth. Congenital cytomegalovirus infection was identified in 76 infants, and as of September 1986 CNS symptoms have been experienced by nine of them. In at least seven of these infants, the disturbances can be referred to the cytomegalovirus infection. The strains from eight of the nine infants have been further studied by restriction endonuclease analysis of cytomegalovirus DNA. The cleavage patterns obtained with BamHI, EcoRI, and HindIII showed a unique pattern for each one of the eight strains. No common pattern could be associated with these eight strains in comparison with strains from postnatally infected children.