Cytomegalovirus (CMV) causes asymptomatic infection in most individuals but can produce devastating illness in immunocompromised hosts and in a small proportion of congenitally infected babies. New techniques in molecular biology have provided insights into the epidemiology and transmission of CMV. Children in day care, their parents, and sexually active individuals, especially homosexual men, are now known to be at particular risk for acquiring CMV. Recent studies show that the risk of CMV acquisition by health care workers is similar to the risk to the general public. Health care workers should be aware of the wide range of clinical manifestations, methods of laboratory diagnosis, and current limitations of treatment of CMV. Careful handwashing and avoidance of excretions and secretions are recommended to decrease the transmission of CMV in the hospital.