Advances in investigative techniques have led to increasing reports of Crohn's disease in CF patients. A retrospective review of the literature on IBD in CF showed findings characterized by ileocolitis with fistula formation; 83% required surgery. A prospective survey of 11,321 CF patients attending 49 CF centers revealed 28 with IBD (25 Crohn's, three ulcerative colitis), ages 4-20 years, mean 15.6 years. The prevalence rate of IBD (247/10(5)) was 7x controls and was accounted for by Crohn's disease (221/10(5)) which was 17x controls. The mechanisms that predispose CF patients to Crohn's disease are discussed.