Background: Inflammatory bowel disease (IBD) is associated with a higher prevalence of opportunistic infections. Epstein-Barr virus (EBV) is a ubiquitous virus related to several malignancies, namely lymphoma; its prevalence in patients with IBD and its relation with different therapeutic regimens are not well studied. Methods: Patients followed in our IBD outpatient clinic were consecutively enrolled for participation in a prospective study, and healthy volunteers were recruited as controls. EBV DNA was measured at least 1 time in each patient. Results: Three hundred and seventy-nine individuals were enrolled in the study (93 treated with 5-aminosalicylates, 91 with azathioprine, 70 with infliximab, 43 with combined treatment with infliximab and azathioprine, and 82 controls). More than 90% of the patients had previous EBV exposure. EBV DNA was found in 132 samples (35%); its prevalence was significantly higher in every group of patients with IBD, comparing to controls. Among patients with IBD, infliximab with or without azathioprine was related to higher prevalence of EBV comparing to azathioprine alone or 5-aminosalicylates (P < 0.05). Age above 60 years was related to EBV DNA positivity with a specificity of 92%. Concerning treated groups, ulcerative colitis was the only risk factor identified for high levels of EBV DNA (>1000 and 2500 copies per milliliter). No relationship was found between EBV and C-reactive protein. Conclusions: IBD is a risk factor for the presence of EBV DNA in blood, particularly in older patients and in those taking infliximab. C-reactive protein was not related to EBV DNA prevalence.@en