Cystic fibrosis (CF) is an autosomal recessive inherited disorder that affects approximately 30,000 North Americans. Defects in the CF transmembrane conductance regulator (CFTR) gene lead to altered secretions from exocrine glands and the pulmonary airways, to a heightened susceptibility to airway infections with Pseudomonas aeruginosa, and to severe airway inflammation. Early attempts to develop a genetic therapy for CF have not met with great clinical success, but these efforts have driven the development of viral gene transfer technology for in vivo gene delivery. The recombinant adeno-associated virus (rAAV) system has proven to be safe for in vivo gene delivery in the airways of experimental animals and CF patients, although potential barriers to delivery have been identified. These barriers may limit the transduction efficiency of this vector, especially in the context of the inflamed airways of adolescent and adult CF patients. We anticipate that the use of alternative rAAV serotype capsids and other vector alterations, along with targeting the lungs of CF patients in the earlier stages of their disease, might eventually allow for these potential limitations to be overcome.