BackgroundThe presence of comorbid conditions could impact performance in pulmonary rehabilitation (PR) programmes. We aimed to compare the comorbidity prevalence among those with chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) and evaluate the impact on PR response.MethodsWe performed a retrospective cohort study, recording comorbidities for all patients with COPD or ILD referred to PR. Participants were classified as responders to PR if they met the minimal important difference for exercise capacity and health-related quality of life (HRQoL). The prevalence of comorbidities and impact on PR outcomes were compared by lung disease and by sex using a univariate analysis and multivariate logistic regression.ResultsThe mean number of comorbidities was similar among those with COPD (3.3±2.1, n=242) and ILD (3.2±1.9, n=66) (p>0.05). Females had a higher number of comorbidities than males in both COPD (p=0.001) and ILD (p=0.017) populations. Circulatory (64%) and endocrine/metabolic (45%) conditions were most common in COPD. In ILD, digestive (55%) and circulatory (53%) comorbidities were most prevalent. In people with ILD, those over 65 years, with musculoskeletal/connective tissue disease or circulatory disease were less likely to obtain meaningful improvements in exercise capacity. There was no impact of comorbidities on exercise capacity in COPD or on HRQoL in ILD.ConclusionsThe majority of patients with COPD or ILD enrolled in PR programmes have multiple comorbidities that may affect improvements in exercise capacity. PR programmes may be less effective for older adults with ILD and comorbid circulatory or musculoskeletal disease.