Hepatobiliary disease complicates cystic fibrosis (CF) and may lead to end stage liver disease. Early detection of liver disease with identification of candidates/therapies such as bile acids may prevent long-term morbidity and mortality. This three-center study is designed to perform serial measurements of standard liver function tests and serum bile acids in CF to determine the role of serum bile acid measurements in identifying CF patients with early liver disease. Sixty outpatient visits have been made and data is incomplete. It is anticipated that enrollment and follow-up will be completed within 12-24 months.