Cytomegalovirus is a herpesvirus that commonly infects humans. It can cause enlarged cells (cytomegalic inclusion disease) and poses a risk for severe infections in infants during pregnancy or birth as well as immunosuppressed individuals. The virus replicates slowly in human fibroblasts and establishes lifelong latent infections. Primary infection is usually asymptomatic but can resemble mononucleosis. Congenital infection may cause death, growth problems, or long-term neurological and vision issues in infants. Polymerase chain reaction testing and antigen detection are now used to diagnose active cytomegalovirus infections.