Background: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life-threatening disease caused by chronic dysregulation of the complement system. PNH has a high symptom burden with significant impacts on the life of a patient. The PNH Symptom Questionnaire (PNH-SQ) is a PNH-specific patient-reported outcome (PRO) questionnaire designed to assess daily symptom severity in patients with PNH. The objective of this current study was to evaluate PNH-SQ psychometric properties among patients with PNH from three phase 2 clinical trials with pozelimab monotherapy or in combination with cemdisiran.