Pulmonary Langerhans cell histiocytosis (PLCH) determines reduced exercise capacity. The speculated mechanisms of exercise impairment in PLCH are ventilatory and cardiocirculatory limitations, including pulmonary hypertension (PH).What are the mechanisms of exercise limitation, the exercise capacity and the prevalence of dynamic hyperinflation (DH) and PH in PLCH?In a cross-sectional study, PLCH patients underwent an incremental treadmill cardiopulmonary exercise test with an evaluation of DH, pulmonary function tests, and transthoracic echocardiography. Those patients with lung diffusing capacity for carbon monoxide (DLCO) less than 40% predicted and/or transthoracic echocardiogram with tricuspid regurgitation velocity (TRV) greater than 2.5 m/s and/or with indirect PH signs underwent right heart catheterization.Thirty-five patients were included (68% women, 47 ± 11 years old). Ventilatory and cardiocirculatory limitations, impairment suggestive of PH, and impaired gas exchange occurred in 88%, 67%, 29%, and 88% of patients, respectively. The limitation was multifactorial in 71%, exercise capacity was reduced in 71%, and DH occurred in 68% of patients. Forced expiratory volume in the first second (FEV1) and DLCO were 64 ± 22% predicted and 56 ± 21% predicted, respectively. Reduction in DLCO, an obstructive pattern, and air trapping occurred in 80%, 77%, and 37% of patients, respectively. FEV1 and DLCO were good predictors of exercise capacity. The prevalence of PH was 41%, predominantly with pre-capillary pattern, and mean pulmonary artery pressure correlated best with FEV1 and TRV.PH is frequent and exercise impairment is common and multifactorial in PLCH. The most prevalent mechanisms include ventilatory, cardiocirculatory, and suggestive of PH limitations.