Background and PurposeMultidimensional tools could evaluate the dyspnea of patients with chronic lung disease. The aim was to validate the use of the French–Canadian version of the modified dyspnea index (MDI) among patients with pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD).MethodsThe Spearman test analyzed the convergent validation of the MDI with pulmonary function tests (PFTs), New York Heart Association (NYHA) functional classification, the Modified Borg Scale, the Veterans Specific Activity Questionnaire (VSAQ), physical capacity, physical activity (Godin-Shephard Leisure-Time Physical Activity Questionnaire [GSLTPAQ]), and quality of life (SF-12).ResultsThe MDI had a low correlation with PFT and physical activity; a moderate with physical capacity; a high with the physical dimension (SF-12).ConclusionThe results support the convergent validation of the MDI French–Canadian version with PAH or ILD.