BackgroundCystic fibrosis (CF) is a genetic, multisystemic, progressive and life-shortening disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. Different genotypes have been linked to variations in disease progression among people with CF. The burden of illness (BOI) in children with CF is incompletely characterised, particularly as it relates to CFTR genotypes prior to the availability of the first CFTR modulators. This retrospective, cross-sectional, descriptive study evaluated the BOI in US children with CF MethodsData from the US Cystic Fibrosis Foundation Patient Registry from 2011 were used to summarise key patient and disease characteristics using descriptive statistics, overall and grouped by age (0 to F508del/F508del, F508del/minimal function (MF), MF/MF, gating mutation on ≥1 allele, residual function mutation on ≥1 allele and R117H on ≥1 allele) group.ResultsThe analysis included 9185 children. Among 6-year-olds to 1 in 1 s was 92.6% (17.5%). Among all children ConclusionsPrior to the approval of the first CFTR modulator therapies in children