Primary Ciliary Dyskinesia (PCD) is a rare genetically heterogeneous disorder which results from dysfunction of motile hair-like organelles (cilia) that results in severe, chronic airways disease. Due to other cilia-related disease mechanisms several other organ systems like the heart can be affected. The complexity of the disease phenotype, late diagnosis, as well as lack of evidence based management guidelines contribute to a high burden of disease and cause high health care costs.Therefore, there is a great need for observational trials as well as well-designed randomised controlled trials to put evidence-based diagnostic and treatment approaches into effect.The main objective of our project is to improve diagnosis and treatment of PCD patients. To accomplish this, we propose to:1) Establish widespread, early diagnosis by introduction of nasal Nitric Oxide measurement as screening tool, and by introduction of high-speed videomicroscopy as diagnostic tool;2) Develop new outcome criteria, especially a PCD-specific quality of life questionnaire, as a prerequisite for controlled PCD trials;3) Establish a PCD registry for both cross-sectional analysis of current disease status and longitudinal observational analysis of disease progression under different regimens;4) Generate evidence-based treatment guidelines by conducting two prospective randomized trials on the inhalation of hypertonic saline and long term azithromycin therapy.To achieve these goals members of the European Respiratory Society’s PCD task force will join forces with members of the NIH-funded US-PCD-network.In our multi-national project, we will for the first time establish evidence-based guidelines for diagnosis, clinical management and therapy. We expect that in a high proportion of children the diagnosis will be established before irreversible lung damage has occurred. In later diagnosed individuals the disease burden will be reduced and chronic respiratory failure retarded.