Patients with precapillary pulmonary hypertension (PPH) have classically been reported to have normal pulmonary mechanical function. We reviewed spirometric data from 8 patients with primary pulmonary hypertension and from 17 patients with chronic thromboembolic pulmonary hypertension. All patients had undergone right heart catheterization and pulmonary angiography. Five of the 8 patients with primary pulmonary hypertension demonstrated a severe restrictive ventilatory pattern with a mean vital capacity (VC) of 50.4% predicted and a mean total lung capacity (TLC) of 64.3% predicted. Five of the 17 patients with chronic thromboembolic pulmonary hypertension manifested a restrictive pattern with a mean VC of 68.0% predicted and a mean TLC of 75.3% predicted. We conclude that restrictive ventilatory defects occur more frequently than previously described in patients with PPH. The physiologic mechanism responsible for the restrictive ventilatory pattern is not clear.