The general characteristics of cytomegalovirus (CMV), one of a member of the family Herpesviridae has been described. Epidemiologic findings, especially CMV infection rates in normal individuals and different risk groups, as well as sources of infection have been discussed. The article presented clinical syndromes associated with CMV infection in normal host, infants, blood products and allograft recipients, HIV-positive and undergoing immuno-suppressive therapy patients.