In contradiction to the rule that PH is mild and occurs in patients with more severe obstructive lung disease, a subset of COPD patients exhibit disproportionately severe PH (mean PAP > 40 mm Hg). Severe PH was identified in 27 of 998 COPD patients undergoing right-heart catheterization.3 Eleven patients (1.1%) had no other identifiable cause of PH. Similar to our patient, patients with severe PH had moderate airflow obstruction (median FEV1, 50% of predicted), a very low diffusing capacity of the lung for carbon monoxide, severe hypoxemia, and hypocapnia. Thabut et al2 performed right-heart catheterization in 215 patients with severe COPD (mean FEV1, 24.3% of predicted) referred for lung volume reduction surgery or lung transplantation. Cluster analysis revealed 16 patients (7.4%) with severe PH (mean PAP > 45 mm Hg). Compared to the group as a whole, the patients with severe PH had less severe airflow obstruction (mean FEV1, 48.5% of predicted) and severe hypoxemia (mean Pao2, 46 mm Hg).