Cytomegalovirus (CMV) is a double-stranded DNA herpesvirus. The Centers for Disease Control and Prevention (CDC) estimates that 50% to 85% of adults are infected by age 40. The incubation period for primary infection is 4 to 8 wk. Transmission may occur by direct contact with oral, respiratory, or venereal secretions and excretions. CMV infection is of primary concern in pregnant or immunocompromised patients or patients who have recently received an organ transplant. Blood units are sometimes tested for the presence of CMV if patients in these high-risk categories are the transfusion recipients. CMV serology is part of the TORCH (toxoplasmosis, other [congenital syphilis and viruses], rubella, CMV, and herpes simplex type 2) panel used to test pregnant women. CMV, as well as these other infectious agents, can cross the placenta and result in congenital malformations, abortion, or stillbirth. The presence of immunoglobulin (Ig) M antibodies indicates acute infection. The presence of IgG antibodies indicates current or past infection. There are numerous methods for detection of CMV. The methodology selected is based on both the test purpose and specimen type. Other types of assays used to detect CMV include direct fluorescent assays used to identify CMV in tissue, sputum, and swab specimens; hemagglutination assays, cleared by the FDA for testing blood prior to transfusion; polymerase chain reaction (PCR), used to test a wide variety of specimen types, including amniotic fluid, plasma, urine, CSF, and whole blood; and cell tissue culture, which remains the gold standard for the identification of CMV.