RESUMEN
Infection and disease due to cytomegalovirus (CMV) is one of the upsurging problems in infectious diseases. CMV ranges number one in congenital infections of man and is the main cause of infectious complications in transplant recipients. The complete epidemiological pattern of CMV is still unknown, but there does not seem to be an unique route for its transmission since it can be isolated from saliva, tears, urine, milk, endometrial secretions, semen and faeces. Which route is most important is unknown but there is circumstancial evidence suggesting that up to 12% of people acquire the infection from a maternal source; most people are infected horizontally from playmates at the day care center or kindergarten age or venereally, since the prevalence of the infection increases after puberty. One of the most intriguing problems of CMV is its mechanism of reactivation after transplantation; classically it was considered that reactivation was due to therapeutic immunosupression associated to transplants, but it is becoming clear that allogeneic stimulation may by itself be the cause of reactivation.