['To compare three existing endoscopic scoring systems and a newly proposed modified scoring system for the assessment of patients with chronic rhinosinusitis (CRS).', 'Blinded, prospective cohort study.', 'CRS patients completed two patient-reported outcome measures (PROMs)-the visual analogue scale (VAS) symptom score and the Sino-Nasal Outcome Test-22 (SNOT-22)-and then underwent a standardized, recorded sinonasal endoscopy. Videos were scored by three blinded rhinologists using three scoring systems: the Lund-Kennedy (LK) endoscopic score; the Discharge, Inflammation, Polyp (DIP) score; and the Perioperative Sinonasal Endoscopic score. The videos were further scored using a modified Lund-Kennedy (MLK) endoscopic scoring system, which retains the LK subscores of polyps, edema, and discharge but eliminates the scoring of scarring and crusting. The systems were compared for test-retest and inter-rater reliability as well as for their correlation with PROMs.', 'One hundred two CRS patients were enrolled. The MLK system showed the highest inter-rater and test-retest reliability of all scoring systems. All systems except for the DIP correlated with total VAS scores. The MLK was the only system that correlated with the symptom subscore of the SNOT-22 in both unoperated and postoperative patients.'] Does modification of the Lund-Kennedy endoscopic scoring system improve its reliability and correlation with patient-reported outcome measures?