Ivacaftor (Kalydeco(?), Vertex Pharmaceuticals) is the first of a new class of drugs that target the underlying protein defect in cystic fibrosis (CF). It is aimed at patients with the G551D (glycine to aspartate change in nucleotide 1784 in exon 11) mutation; 5.7% of patients with CF in the UK have this mutation.To review the clinical effectiveness and cost-effectiveness of ivacaftor for the treatment of CF in patients aged ? 6 years who have the G551D mutation.Ten databases, including MEDLINE and EMBASE, were searched from inception to July 2012. Studies that evaluated ivacaftor for the treatment of adults and children (? 6 years) with at least one G551D mutation were eligible. There were insufficient data to conduct a formal meta-analysis. The manufacturer of ivacaftor, Vertex Pharmaceuticals, submitted a deterministic patient-level simulation model for the assessment of the lifetime cost-effectiveness of ivacaftor. We modified the model where values were not UK-specific or not recent, or where better estimates could be found. The only change to the model structure was the addition of lung transplantations. We changed utility values, annual decline in percentage predicted forced expiratory volume in 1 second (FEV1), and the baseline exacerbation rate, and used data from the CF Registry to estimate the relation between costs, age and percentage predicted FEV1. Estimates of treatment effect of ivacaftor came from the clinical effectiveness review. We modelled three scenarios for the longer-term effects of ivacaftor. We also modelled an 'optimistic' scenario for patients aged <12 years with little lung damage. We conducted a budget impact analysis to estimate the total cost to the NHS of introducing ivacaftor in England.Three studies were included: a randomised controlled trial (RCT) in adults (n = 167) (? 12 years), a RCT in children (n = 26) (6-11 years), and an open-label extension study of the two RCTs. Both RCTs reported significantly greater changes from baseline in all measures of lung function in patients receiving ivacaftor than in those receiving placebo. The mean difference in change in percentage predicted FEV1 was 10.5 [95% confidence interval (CI) 8.5 to 12.5] percentage points in the adults' study and 10.0 (95% CI 4.5 to 15.5) percentage points in the children's study at 48 weeks. Improvements in lung function were seen across all subgroups investigated (age, sex, study region and lung function). There were significantly greater improvements in the ivacaftor group than in the placebo group for all outcomes assessed (exacerbations, quality of life, sweat chloride and weight) with the exception of quality of life in children. Improvements were maintained in the open-label trial. Adverse events were mainly minor and comparable across treatment groups. Both RCTs reported more withdrawals in the placebo group than in the ivacaftor group. The incremental cost-effectiveness ratio varied between ?335,000 and ?1,274,000 per quality-adjusted life-year gained. The total additional lifetime costs for all eligible CF patients in England ranged from ?438M to ?479M; the lifetime cost for standard care only was ?72M.The available evidence suggests that ivacaftor is a clinically effective treatment for patients with CF and the G551D mutation; the high cost of ivacaftor may prove an obstacle in the uptake of this treatment. The main priority for further research is the long-term effectiveness of ivacaftor.This study is registered as PROSPERO CRD42012002516.The National Institute for Health Research Health Technology Assessment programme.