Cystic fibrosis (CF) is the commonest, fatal, autosomal recessive disorder and is associated with lung sepsis, pancreatic failure and elevated sweat electrolytes. The CF gene on chromosome 7 encodes a protein identified as CF transmembrane conductance regulator (CFTR) which regulates chloride ion transport in epithelial cell membranes. Almost 100 mutations have been identified in this gene which cause defective chloride-channel control. Recently, this abnormality has been reversed in affected CF cells in vitro by retrovirus-mediated transfer of a normal gene. Fifty years ago, most cases died in childhood, but now up to 80% reach adulthood. Chronic lung sepsis is the principal cause of death, and intensive antibiotic therapy with chest physiotherapy is used to control this. Advanced lung disease can be successfully treated by heart-lung transplantation. Nebulised recombinant DNase and antineutrophil elastase agents such as alpha-1-antitrypsin and secretory leucoprotease inhibitor are potentially promising new therapies. Pancreatic insufficiency is managed by high-calorie diets and enteric coated enzyme supplements. Other prominent gastrointestinal complications include meconium ileus equivalent, biliary cirrhosis and cholelithiasis. Specially dedicated CF centres have led to improved survival rates and allow experienced staff to treat the many complications of CF while promoting research in this multisystem disorder.