We report a 35-year-old man, a renal allograft recipient, who presented with toxic megacolon. Segmental biopsies from the colon were consistent with cytomegalovirus colitis. Serum polymerase chain reaction for cytomegalovirus DNA confirmed the diagnosis. He was treated with ganciclovir but, though his abdominal condition improved initially, he worsened later and succumbed to his illness.