Cystic fibrosis (CF) is the most common lethal inherited disease in the white population. It is caused by the absence or dysfunction of the multifunctional CF transmembrane conductance regulator (CFTR) protein. More than 1,000 mutations of the CFTR gene divided into six classes have been described. Current treatments for CF manage complications and symptoms, rather than the cause of the disease. However, there are several orally active compounds under development – CFTR modulators – that aim to correct the underlying gene defect that leads to CF by modifying the function of the CFTR protein. Since the therapeutic effects of CFTR modulators are based on individual protein defects, knowledge of the genotype of both alleles of the CFTR gene is necessary for appropriate patient selection. At present there are only a few CFTR modulators which have completed the third phase of clinical trials and have been approved for use. Unfortunately, their clinical effectiveness seems to be modest. At present, due to extremely unfavourable cost-benefit ratio, the lumacaftor-ivacaftor combination can not be recommended for CF patients who are homozygous for F508del CFTR mutation. Further efforts are needed to develop the next generation of CFTR modulators with more effective modifying potential.