RATIONALE: Spirometry in children with cystic fibrosis (CF) frequently fails to return to baseline after treatment for a pulmonary exacerbation. It is unclear whether the same is true for children with primary ciliary dyskinesia (PCD). OBJECTIVES: To determine in children with PCD treated with intravenous antibiotics for a pulmonary exacerbation: (1) the proportion who recover to baseline forced expiratory volume at 1 sec (FEV1 ) within 3 months after treatment and (2) to try to identify factors which are associated with failure to regain pre-exacerbation FEV1 . METHODS: Cohort study using the PCD database for children at the Royal Brompton Hospital, 2003-2013. We selected the first pulmonary exacerbation treated with intravenous antibiotics. The best FEV1 within 3 months after treatment was compared to the best FEV1 in the 12 months before treatment (baseline). Recovery to baseline was defined as any FEV1 after treatment that was greater than or equal to 90% of the baseline FEV1 . RESULTS: 32/150 children (21%) had at least one pulmonary exacerbation. 23/30 (77%) regained baseline spirometry within 3 months of treatment. There was no difference between responders and non-responders in any baseline characteristics. CONCLUSIONS: Around 25% of children with PCD fail to recover to baseline lung function within 3 months following treatment for a pulmonary exacerbation, similar to CF. Better treatment strategies are needed, and the results also suggest that prevention of exacerbations would be a useful end-point in clinical trials. Pediatr Pulmonol. 2016;9999:XX-XX. © 2016 Wiley Periodicals, Inc.