C. difficile (C. d.) is the main cause of antibiotic-associated diarrhea and colitis. It is shown in literature a high asymptomatic carriage rate of C. d. in patients with cystic fibrosis (CF), though C. d.-related colitis is an uncommon complication in these patients, despite the use of multiple high-dose antibiotic regimes and the frequency of hospital admissions. Lung transplantation with the associated immunosuppression and aggressive antibiotic therapy may increase the risk of the clinical manifestation of C. d. In this paper, we describe three cases of severe C. d. colitis in patients with CF following lung transplantation and illustrate our experience in the diagnosis and management of these patients.