A variety of cholestatic liver diseases appear to primarily affect the biliary epithelium, including cystic fibrosis (CF). CF results from a defect in the chloride channel protein, cystic fibrosis transmembrane conductance regulator (CFTR). Although the majority of CF patients have a genomic deletion in deltaF508, other mutations of CFTR may result in less severe clinical presentations and outcomes. Recently, CFTR has been shown to be involved in secretin-stimulated choleresis in intrahepatic bile duct epithelial cells. Cholestasis in cystic fibrosis appears to result from defective chloride transport across the biliary epithelium and is the only cholestatic disease of bile ducts for which a cellular defect has been identified. Primary sclerosing cholangitis (PSC) is a cholestatic disease with histological and cholangiographic features similar to CF. The purpose of this pilot study was to explore whether there is an increased prevalence of CFTR mutations. Two patients exhibited mutations in one allele, yielding a carrier rate of 10.6%, not statistically different from the general U.S. population carrier rate of 4%.