We present three lung transplant recipients who had sigmoid colonic diverticular perforation within 4 weeks of transplantation, giving an overall incidence of 8.6% (3 of 35) in our population. Our cases are unusual because they all occurred in the early posttransplantation period and because the incidence of perforation is substantially higher than that reported in other transplant populations. The reason for the apparent increased incidence of perforation in our lung transplant recipients is unclear, but it is likely related to the short follow-up period, intense posttransplantation immunosuppression, perioperative hypoperfusion, and increased intraluminal pressure from the use of narcotics and bowel stimulants. We discuss these potential causes and comment on preventive measures being undertaken at our program.