Immunosuppressive agents (azathioprine, methotrexate) are increasingly being used in the treatment of inflammatory bowel disease. The use of immunosuppressive agents is associated with a greater risk of opportunistic infections, the most frequent of which are those caused by cytomegalovirus and varicella zoster virus. We present four cases of opportunistic infections due to Herpesviruses in patients undergoing immunosuppressive treatment with azathioprine for Crohn's disease. We also review the literature published on this topic. Two patients presented cutaneous varicella complicated by pneumonia and esophagitis respectively, one patient had cutaneous herpes zoster and the other had fatal pneumonia possibly caused by the Herpesvirus. In the first three the clinical course of the infection was favorable after withdrawing immunosuppressant treatment and initiating treatment with aziclovir. In patients Crohn's disease azathioprine treatment increases the risk of opportunistic infection by Herpesvirus. However, in the absence of other factors that increase immunosuppression, these infections usually have a benign course with specific antiviral therapy.