Cystic fibrosis (CF), the most common lethal autosomal recessive disease in white populations, is characterized by dysfunctional chloride ion transport across epithelial surfaces. Although recurrent pulmonary infections and pulmonary insufficiency are the principal causes of morbidity and death, gastrointestinal symptoms commonly precede the pulmonary findings and may suggest the diagnosis in infants and young children. The protean gastrointestinal manifestations of CF result primarily from abnormally viscous luminal secretions within hollow viscera and the ducts of solid organs. Bowel obstruction may be present at birth due to meconium ileus or meconium plug syndrome. Complications of meconium ileus include volvulus, small bowel atresia, perforation, and meconium peritonitis with abdominal calcifications. Older children with CF may present with bowel obstruction due to distal intestinal obstruction syndrome or colonic stricture, and tenacious intestinal residue may serve as a lead point for intussusception or cause recurrent rectal prolapse. Radiologic studies often demonstrate thickened intestinal mucosal folds in older children and uncommonly show colonic pneumatosis, peptic esophageal stricture due to gastroesophageal reflux, and duodenal ulcer. Appendicitis due to inspissated secretions is uncommon. Obstruction of ducts and ductules produces exocrine pancreatic insufficiency, pancreatitis, cholestasis, cholelithiasis, and cirrhosis with portal hypertension. On imaging studies, the pancreas is commonly small and largely replaced by fat, sometimes displays calcifications, and is rarely replaced by macrocysts. Radiologic features of hepatobiliary disease include an enlarged radiolucent liver from steatosis, gallstones, a shrunken nodular liver, splenomegaly, and portosystemic collateral vessels. With the improved survival of CF patients, an increased risk for developing gastrointestinal carcinomas has been established, many occurring as early as the 3rd decade.