Importance:Vitamin A(or retinol)has considerable antioxidative and anti-inflammatory attributes and it may have protective effects on the respiratory health of patients with cystic fibrosis(CF).This issue,however,remains controversial.Objective:The purpose of the present study was to investigate the relationship between serum retinol levels(SRL)and force expiratory volume in 1 second(FEV1)in patients with CF.Methods:All patients with pancreatic insufficiency attending the CF Department of"Agia Sofia"Children's Hospital in Athens,Greece,aged 6 to 19 years during the 2012-2016 period,who could perform spirometry effectively,were included in the study.The impact of SRL on FEV1 was examined longitudinally and analyzed with generalized estimating equations.Results:The study included 231 patients and 851 SRL measurements were performed.In 25(3.2%)cases the SRL were below the 5th percentile of reference distribution;none was above the 95th percentile.The analysis showed that SRL was positively correlated with the FEV1(P<0.001).Interpretation:In this sample of children and adolescents with CF,vitamin A deficiency was rare.Our results suggest a positive relationship between SRL and FEV1.