Four patients are described with pneumatosis intestinalis following cadaveric kidney transplantation, all with severe cytomegalovirus (CMV) infection. Two patients had a primary infection and 2 patients had a reactivation of CMV. One patient died because of disseminated CMV infection. Multiple inclusion bodies were found at postmortem examination in lungs and liver, and at the site of the ulcers in the gastrointestinal tract. Two patients had, concomitantly, an active, nonobstructive duodenal ulcer. In a control population of 17 patients who suffered from a duodenal ulcer post-transplant without any evidence of CMV-infection, we could not demonstrate pneumatosis intestinalis. We suggest a possible causal relationship between pneumatosis intestinalis and active CMV infection. The mechanisms that could be responsible for this relationship are discussed.