The purpose of this study was to evaluate the safety and efficacy of ivacaftor in participants with cystic fibrosis (CF) who were aged 12 years or older and were homozygous for the F508del-CF transmembrane conductance regulator (CFTR) mutation. Ivacaftor is a potent and selective CFTR potentiator of wild-type, G551D, F508del, and R117H forms of human CFTR protein. Potentiators are pharmacological agents that increase the chloride ion transport properties of the channel in the presence of cyclic adenosine monophosphate (AMP)-dependent protein kinase A (PKA) activation.