METHODS: We validated a scoring system in 128 children with CF and 90 age-matched controls. CT scans were blindly interpreted by 3 physicians (pulmonologist, otolaryngologist, and a neuro radiologist) on two separate occasions. Intra-rater and inter-rater reliability were measured by intraclass correlations (ICC). CT scoring system: The following parameters were included in the score: Maxillary opacification (MO), Nasal cavity obstruction (NCO), Lateral nasal wall displacement (LNWD), Uncinate process (UP) absence or demineralization, and Mucocele (MU). The right and left sides were scored separately. Maxillary opacification and nasal cavity obstruction were scored in a graded fashion (0 to 3) with 0 = normal, 1 = mild (<33%), 2 = moderate (33-66%) and 3=severe (>66%). Lateral nasal wall displacement, Uncinate process absence/ demineralization, and Mucocele were scored as 1=present, 0=absent.