Developmental and behavioral problems in preschool-aged primary ciliary dyskinesia patients Abstract Primary ciliary dyskinesia (PCD) causes a broad spectrum of disease. This study aims to explore the developmental, behavioral, and social-emotional aspects of preschool-aged children with PCD. Fourteen PCD, 17 cystic fibrosis (CF) patients and 15 healthy subjects were enrolled. Developmental features of the participants were evaluated with Ages and Stages Questionnaire. Parents of participants filled out the Child Behavior Checklist (CBCL). The number of children screened positive for developmental delay was statistically higher in the PCD group. Higher numbers of children with PCD were screened positive for developmental delay in communication and problem-solving domains. Delay in fine motor skill domain was more common in children with PCD and CF compared to healthy subjects. There was no difference among the three groups in terms of gross motor and personal-social development. None of the children in all three groups was shown to have social-emotional problems. In CBCL, patients with CF had higher internalizing problem scores. Externalizing and total problem scores did not differ between the three groups. However, among PCD patients, children with developmental delay on more than one domain had higher externalizing and total problem scores. Conclusion: The current study revealed that positive screening for developmental delay is more common in preschool-aged PCD patients compared to patients with CF and healthy children. What is Known: • Intelligence scores of school-aged PCD patients are similar to healthy subjects despite their higher internalizing problem scores on Child Behavior Checklist (CBCL). • School-aged PCD patients exhibit higher hyperactivity and inattention findings. What is New: • Positive screening for developmental delay in communication, problem-solving and fine motor skills is more common in preschool-aged PCD patients. • Preschool-aged PCD patients screened positive for developmental delay in more than one domain have higher externalizing and total problem scores on CBCL.