Cystic fibrosis (CF) is caused by mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator, CFTR. Previously we demonstrated that the common delta F508 mutation in the first nucleotide binding domain (NBD1) alters the ability of the domain to fold into a functional three-dimensional structure, providing a molecular explanation for the observation that the mutant CFTR is retained in the endoplasmic reticulum and does not traffic to the apical membrane of affected epithelial cells. Notably, when conditions are altered to promote folding of the mutant protein, it can assume a functional conformation. Correcting the folding defect may have therapeutic benefit for the treatment of cystic fibrosis. Here we summarize these results and discuss the implications in vitro folding studies have for understanding the pathobiology of CF.