Pulmonary hypertension is a common complication of chronic obstructive pulmonary disease (COPD). The increase in pulmonary artery pressures is often mild to moderate, but some patients may suffer from severe pulmonary hypertension, and present with a progressively downhill clinical course because of right-sided heart failure added to ventilatory handicap. The cause of pulmonary hypertension in COPD is generally assumed to be hypoxic pulmonary vasoconstriction leading to permanent medial hypertrophy. However, recent pathological studies point, rather, to extensive remodeling of the pulmonary arterial walls, with prominent intimal changes. These aspects account for minimal reversibility with supplemental oxygen. There may be a case for pharmacological treatment of pulmonary hypertension in selected patients with advanced COPD and right-sided heart failure. Candidate drugs include prostacyclin derivatives, endothelin antagonists and inhaled nitric oxide, all of which have been reported of clinical benefit in primary pulmonary hypertension. However, it will be a challenge for randomized controlled trials to overcome the difficulties of the diagnosis of right ventricular failure and the definition of a relevant primary endpoint in pulmonary hypertensive COPD patients.