Knowledge of the natural history of symptomatic congenital cytomegalovirus (CMV) infection in the newborn is essential in order to anticipate complications and assess the potential benefit from antiviral therapy. To define the disease course we reviewed data on 106 neonates with symptomatic congenital CMV infection diagnosed and managed by the investigators. Petechiae, jaundice and hepatosplenomegaly were each noted in 70% or more patients. Microcephaly was noted in 54 of 102 (53%) at birth. Elevated alanine aminotransferase, con jugated hyperbilirubinemia and thrombocytopenia were seen in 83, 81 and 77%, respectively. Eighty-six percent had at least two of the manifestations highly suggestive of congenital infection. Platelet count fell to its nadir during the second week of life whereas elevated alanine aminotransferase and direct bilirubin persisted past the first month. In spite of the difficulty in assessing central nervous system function in the newborn, evidence of damage was present in the majority. Seventy-two had microcephaly, poor suck, lethargy/hypotonia or seizures. Abnormal computerized tomographic scan was present in 16 of 20 (80%) and decreased hearing in 20 of 39 (56%). Cerebrospinal fluid protein was >120 mg/dl in 24 of 52 (46%) and this elevation was associated with neurologic abnormalities as well as hearing loss. The mean length of hospital stay was 13 and 22.4 days for term and preterm infants, relatively. Thirteen infants (12%) died during the first 6 weeks of life. Disseminated CMV infection with multiorgan involvement was evident in 7 of 9 at postmortem examination. We conclude that neonates with symptomatic congenital CMV infection have a multisystem disease with significant morbidity and mortality. © 1992 by Williams and Wilkins.