Cytomegalovirus (CMV) colitis may cause symptoms and signs identical to those of idiopathic inflammatory bowel disease. Although difficult to diagnose with certainty, the histological finding of cytomegalovirus inclusions in tissue from a case of suspected inflammatory bowel disease is strongly suggestive. CMV colitis is an entity almost entirely confined to cases of severe immunosuppression. The case of a 79 year old widower who was admitted to hospital with symptoms suggestive of inflammatory bowel disease is presented. Despite medical treatment his condition worsened and he developed toxic dilatation of the colon requiring colectomy. Histological examination showed a mild superficial pancolitis, with focal severe inflammation, deep fissuring ulceration, and pseudopolyposis. Abundant CMV inclusions were seen in cells associated with the ulcerating inflammatory tissue. A diagnosis of indeterminate colitis with CMV was made. The patient's condition worsened after surgery and he died a few days later despite intensive treatment, including antiviral chemotherapy directed against CMV. After death HIV serology was found to be positive. Regardless of the age and perceived lifestyle of the patient, a diagnosis of CMV colitis in someone not known to be immunosuppressed raises the possibility of HIV infection.