Today, the majority of cystic fibrosis (CF) patients treated in Germany have reached adulthood. However, with increasing age the morbidity and frequency of severe pulmonary complications continues to rise. Further optimization of conventional therapy alone will be insufficient to compensate for this development. In recent years, there has been impressive progress in our understanding of the molecular basis of the CF gene and its product, the cystic fibrosis transmembrane conductance regulator (CFTR). This knowledge can now be applied to develop new therapeutic strategies. However, important questions remain to be solved, i. e., little is known about the pathways that link the malfunctioning of the CFTR protein with the observed clinical phenotype. This review briefly touches on CF genetics as it applies to lung disease and will focus on the current hypotheses of CFTR (dys)function and its impact on pulmonary fluid homeostasis. New treatment options that target the molecular basis of the disease will be discussed.