Patient-centered outcomes are significantly modified by long-term home non-invasive ventilation (NIV), but a short, self-administered, specific tool for routine clinical assessment is lacking. The aim of this study was to develop and validate the S3-NIV questionnaire, a short questionnaire to measure respiratory s ymptoms, s leep quality and NIV-related s ide-effects.Stable patients under long-term home NIV were recruited from three outpatient NIV services. Questionnaire development consisted of a selection of core items for analysis, followed by item reduction, validation and test-retest reliability.338 patients completed a 22-item questionnaire. Eleven items were removed because of non-scalability (n=2), redundancy (n=8) and lack of fit (n=1). The final version of the S3-NIV questionnaire consisted of 11 items covering two dimensions: "respiratory symptoms" (Cronbach alpha=0.84) and "sleep & NIV-related side-effects" (Cronbach alpha=0.77). Convergent validity was high between the "respiratory symptoms" subscale of the S3-NIV questionnaire and the St. George's Respiratory Questionnaire (rho=-0.76; p<0.001), as well as the "sleep & NIV side-effects" subscale and the Quebec Sleep Questionnaire (rho=0.51; p<0.001). The S3-NIV questionnaire had a good test-retest reliability after 4 weeks (intraclass correlation coefficient=0.72).The S3-NIV questionnaire is a short, valid and repeatable, self-completed tool for the routine clinical assessment of patients undergoing home NIV.