Cytomegalovirus (CMV) is significant for human health as a cause of birth defects and infections in immunocompromised patients. Congenital CMV infection is a leading cause of hearing loss and an important cause of mental retardation and cerebral palsy. CMV is a common opportunistic pathogen for immunocompromised patients, especially those with impaired cell mediated immunity due to acquired or congenital immune deficiency syndromes, hematopoietic stem cell transplantation or solid organ transplantation. CMV shares many structural, functional and biological features with other members of the herpesvirus family, including indefinite persistence in its human host. Unique to CMV is the key role of mother to child transmission during birth and through breast milk in maintaining population prevalence of infection. Horizontal transmission of CMV is linked to activities that involve contact with body fluids from another person, notably care of young children and intimate contact. The most pressing challenge for public health posed by CMV is development of an effective means of preventing congenital CMV disease.