The role of cytomegalovirus (CMV) infection in patients with inflammatory bowel disease (IBD) is controversial. Although CMV has been specifically associated with refractory disease, the strength and nature of this association have been a subject of debate. The aim of this study was to evaluate the prevalence and outcome of acute cytomegalovirus infection in patients with severe refractory and complicated inflammatory bowel disease. Seventy-two patients with active IBD (both ulcerative colitis [UC] and Crohn's diseases [CD]) were included in this study. Thorough history taking and physical examination of all patients was made with special emphasis on symptoms and signs of CMV disease. Colonoscopic assessment was made for the extent and activity of IBD and collection of specimen. Prevalence of CMV infection was estimated by serology; anti-CMV IgM and IgG antibodies, and pathologic studies of colonic biopsies used conventional haematoxylin and eosin (H & E) and immunohistochemistry (IHC) with monoclonal antibodies. Complete blood count and liver function tests were done for all patients. Among 72 patients with active inflammatory bowel disease, 23 (31.9%) were resistant to intravenous steroids. CMV was detected in eight (six with UC and two with CD) of the 23 (34.8%) steroid-resistant patients and in only one (3.2%) patient in the remaining 31 patients under steroid treatment and was not detected in 18 IBD patients not using steroids. Among nine CMV-positive IBD patients, six (66.6%) were female and six had fever; cervical lymphadenopathy was found in five patients and splenomegaly in two, compared to no patients in the CMV-negative group (P = 0.01 and 0.03, respectively). Leucopenia and thrombocytopenia were predominantly seen in the CMV-positive versus CMV-negative patients (2.1+/-0.3 vs. 5.9+/-3.4 and 98+/-34 vs. 165+/-101, respectively). Pancolitis was found in five of nine CMV-positive IBD patients whereas in only two patients out of 63 in the CMV-negative group (P = 0.005). Acute CMV infection in patients with IBD is not rare and is often underestimated. CMV infection in patients with refractory or complicated IBD should be ruled out before aggressive immunosuppressive therapy. High clinical index of suspicion for the association of CMV infection with IBD should be directed towards female IBD patients presenting with fever, lymphadenopathy, splenomegaly, leucopenia, and mild hepatitis. CMV IHC is significantly more sensitive than routine H & E stain and should be considered as part of the routine evaluation of IBD patients with severe exacerbation or steroid-refractory disease before proceeding with other medical or surgical therapy that may not be necessary once the CMV is treated.