Importance: Epistaxis is the greatest cause of morbidity in patients with hereditary hemorrhagic telangiectasia (HHT); because of this, a validated epistaxis-specific quality-of-life instrument for HHT should be made available. Objective: To develop and validate an epistaxis-specific quality-of-life patient-reported outcome measure for HHT. Design, Setting, and Participants: This survey study focused on the development and validation of the Nasal Outcome Score for Epistaxis (NOSE) in HTT (NOSE HHT) outcome measure with data prospectively collected from December 10, 2019, to March 15, 2020. A total of 401 patients were recruited from within the Cure Hemorrhagic Telangiectasia online patient advocacy social media network, the Washington University HHT Center of Excellence, and a randomized clinical trial investigating an intranasal timolol gel for HHT-associated epistaxis. Main Outcomes and Measures: Face and content validity, factor analysis, internal consistency as measured through Cronbach α, construct validity, responsiveness to change, and minimal clinically important difference. Results: The NOSE HHT was developed and validated with a possible score ranging discretely from 0 to 4 for each of the 29 items and a total score ranging continuously from 0 to 4 after dividing by the total number of items answered. A total of 401 participants completed the NOSE HHT. Factor analysis identified 3 factors that matched the a priori specified subgroups of particular aspects of life affected by HHT-associated epistaxis: physical problems (mean [SD] magnitude, 1.59 [0.83]), functional limitations (mean [SD] magnitude, 1.28 [0.84]), and emotional consequences (mean [SD] magnitude, 1.95 [1.02]). The instrument had high internal consistency with an overall Cronbach α of 0.960. Convergent validity determined the total NOSE HHT score to be a strong predictor of disease severity; total NOSE HHT score can be split up into the following epistaxis severity categories: mild (0-1), moderate (1.01-2), and severe (>2). The instrument was found to be sensitive to change, and the minimal clinically important difference for the total NOSE HHT score was 0.46. Conclusions and Relevance: Evaluation of the consistency, reliability, and responsiveness of the NOSE HHT survey found it to be a valid instrument to assess severity and change in epistaxis. Study results suggest that the NOSE HHT survey is clinically applicable and useful as an outcome measure of future HHT-associated epistaxis trials.