['In this study, we aimed to determine the validity and reliability of the Dyspnea-12 questionnaire (D-12) for the assessment of breathlessness in patients with interstitial lung disease (ILD).', 'A total of 101 patients with ILD completed the D-12 (scale range, 0-36, with a high score indicating worse dyspnea), Medical Research Council (MRC) dyspnea scale, St. George Respiratory Questionnaire (SGRQ), and Hospital Anxiety and Depression Scale (HADS) at baseline, and 84 patients completed the D-12 and a global health transition score at follow-up 2 weeks later. D-12 psychometric properties, including floor and ceiling effects, internal consistency, test-retest reliability, and construct validity were examined.', 'The D-12 showed good internal consistency (Cronbach α, 0.93) and repeatability (intraclass correlation coefficient, 0.94). Its scores were significantly associated with MRC grade (r = 0.59; P < .001), SGRQ (symptoms, r = 0.57; activities, r = 0.78; impacts, r = 0.75; total, r = 0.79; P < .001). Factor analysis confirmed the previously determined structure of the D-12 in this patient group.'] Is dyspnea-12 a valid and reliable measure of breathlessness in patients with interstitial lung disease?