Cystic fibrosis (CF) is a genetic disease due to a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel in epithelial cells. There are about 1900 mutations, divided in several groups, for example, stop mutations, mutations affecting the permeability of the channel, and mutations in which the mutated CFTR is recognized as abnormal and destroyed. Pharmacological treatment has become possible for stop mutations (about 10% of the patients), and for a rare mutation affecting channel permeability. For the majority of patients, however, that have a mutation in which the mutated CFTR is destroyed on its way to the cell membrane, research is still in progress, although a number of compounds have been identified that (at least partly) corrects the error in chloride transport.