Aims: Limited data are available on lung function in paediatric and adult patients with Primary Ciliary Dyskinesia (PCD). Published studies typically included few patients and are difficult to compare because of methodological variations. We summarized the evidence in a systematic review. Methods: In a systematic search in Pubmed, Embase and Scopus we identified all studies reporting on lung function of ³10 PCD patients, published since 1980. Results: We identified 588 studies, but only 44 met our inclusion criteria and allowed extraction of lung function data. 24 of them described overlapping populations. The diagnostic criteria varied from clinical diagnosis to full diagnostic testing. All studies presented spirometry results, with the majority (28) reporting on FEV1 expressed as %predicted. Only 5 studies included alternative techniques (e.g multiple-breath washout). Most studies found mild to moderate obstructive patterns, while few reported severe bronchial obstruction. Mean FEV1% was 73% (range: 51-93%). The 12 studies focusing on paediatric patients reported a mean FEV1% of 78% (range 73-88%); the 7 studies on adults reported a mean FEV1% of 58% (35-77%). Only 5 studies presented longitudinal results. Conclusion: These first results suggest reduced FEV1% in adult PCD patients, which will be further quantified in a meta-analysis. To study the natural history of lung function in PCD, we need standardized sensitive lung function measurements applied to representative patient populations covering a large age range. Funding: BESTCILIA FP7 grant 305404, Lungenliga Bern, Lungenliga St. Gallen, Ligue pulmonaire Vaudoise.