BACKGROUND: To evaluate the respiratory functions in children with cat sensitization accompanying allergic respiratory diseases and to compare these with those of healthy controls, as well as within themselves by classifying according to their diseases, domestic cat exposure, and age groups. METHODS: This prospective case-control study included 130 children aged 3-17 years with cat sensitization (CS group) accompanying respiratory allergic diseases and 70 age- and sex-matched healthy controls (HC group). The cases' demographic parameters were recorded, and respiratory functions were analyzed using IOS and spirometry. RESULTS: At IOS evaluation, zR5, R5-20, Fres, and AX values were higher in children in the CS group compared to the HC group ( CONCLUSIONS: Pulmonary resistance was higher and reactance was lower in the entire and peripheral airways in children with cat sensitization accompanying respiratory allergic diseases compared to the healthy controls. Peripheral airway resistance and reactance were more impaired in the asthma group compared to allergic rhinitis. However, peripheral airway resistance and main airway reactance were more impaired in the preschool age group than in the older ones.