Ivacaftor (Kalydeco™) is a potentiator of the cystic fibrosis transmembrane conductance regulator (CFTR) and is the first drug that treats an underlying cause of cystic fibrosis to be licensed for use. Ivacaftor increases the open probability (i.e. gating) of CFTR channels with the G551D mutation, thus enhancing chloride transport, and is indicated in a number of countries for the treatment of cystic fibrosis in patients aged ≥6 years who carry this mutation. This review focuses on pharmacological, clinical efficacy and tolerability data relevant to the use of ivacaftor in this indication. In two 48-week, double-blind, phase III trials in patients aged ≥12 (STRIVE) or 6–11 (ENVISION) years with cystic fibrosis and the G551D mutation, oral ivacaftor 150 mg every 12 h significantly improved lung function relative to placebo, when used in combination with standard care. Significant improvements in pulmonary exacerbation risk (in STRIVE) as well as bodyweight and some aspects of health-related quality of life (both studies) were also seen with the drug versus placebo. Moreover, the beneficial effects of ivacaftor on parameters such as lung function and bodyweight were maintained over up to 96 weeks of treatment in an ongoing open-label extension of these studies. Ivacaftor was generally well tolerated, with headache, oropharyngeal pain, upper respiratory tract infection and nasal congestion being among the most common adverse events. Thus, ivacaftor expands the current treatment options for patients with cystic fibrosis who have the G551D mutation. Its potential for use in patients with other CFTR mutations is also of interest.