Although both PCD and CF are associated with impaired MCC, the type of impairment and its relative contribution to lung damage is different for the two diseases. It was shown that in CF, MCC is preserved in young patients and those with mild lung disease,31 whereas patients with PCD have no MCC from birth, which may explain their neonatal respiratory distress and middle ear problems rarely seen in CF. Cough clearance is well preserved in PCD, whereas in CF it is dramatically decreased (by tenacity), again arguing for immune dysregulation as being most important for the pathogenesis and progress of CF.32,33 The principal problem in CF is probably a hyperinflammatory response.34,35 CF sputum has been shown to be nonviscous, but rather tenacious. This is a surface property that is influenced by polymeric DNA and actin. Bush et al16 compared mucus properties in both diseases, showing that inflammation, measured by IL-8 concentration, was greater in PCD sputa. No significant differences in the sputum biophysical or transport properties were seen; however, survival in patients with PCD was generally better. Another study, by Santamaria et al,17 compared pulmonary HRCT scan scores for patients with PCD and a group of age- and sex-matched patients with CF. They showed that patients with PCD had significantly less structural lung damage than patients with CF. In our study, patients with CF-PI had worse FEV1 and TBS compared with patients with PCD, suggesting that other causes, in addition to impaired MCC, are responsible for the higher pulmonary morbidity in CF. Epithelial cell dysregulation, excessive airway inflammation, and innate immune deficiency in CF were recently described.4,34,35 It is important to note that, in general, patients with PCD receive less intensive therapy,30 and in our experience, many do not adhere to the scheduled visits and to the routine treatments, although there is also published evidence of suboptimal treatment adherence for patients with CF. Standard care for patients with PCD in our center consists of treatment with rotating oral antibiotics, daily inhalations with hypertonic saline, physiotherapy, and monthly follow-up. Many of these modalities are used in CF, although no evidence for their efficacy was demonstrated in PCD.36 Nevertheless, the results of this study show that adults with PCD do have better pulmonary functions, reaffirming that disease progression in most patients is slower than in CF.