CMV infection has been reported in association with some flares of IBD. Its prevalence varies with the method of diagnosis and the severity of IBD. Although the link between CMV and IBD is not clear, the immunomodulator properties of the virus may play a role in the evolution of IBD. Besides the necessity of immunosuppression to treat IBD, inflammation per se can maintain in situ viral replication. Antiviral treatment can be useful in some situations. New molecular methods will permit earlier and more sensitive diagnosis of CMV infection and a better evaluation of treatment efficacy.