This report summarizes knowledge accumulated in a long-term study of congenital and maternal cytomegalovirus (CMV) infection in Sweden. Some new findings are included. We considered diagnostic methods, sources of maternal infection (including occupational risks), roles of primary and secondary maternal infections, transmission to foetuses, incidence, symptoms and prognosis of established congenital infection and relative importance of such infection in infantile sensorineural deafness, microcephaly and type 1 diabetes mellitus. Virus isolation testing was done 1977-1985 on 16,474 newborns. 76 (0.5%) congenitally infected infants were found, 22/76 (29%) with transient neonatal symptoms and 11/60 (18%) with neurological symptoms by the age of 7 y. Type of maternal CMV infection was serologically determined in 62/76 cases (30 primary, 32 secondary). CNS disturbances in the infants occurred after both primary (all trimesters) and secondary maternal infections. The negative potential of secondary maternal infections might be an obstacle to preventive vaccination.