Pulmonary hypertension occurs frequently in patients with chronic lung disease and contributes to morbidity and mortality. The most common symptoms are dyspnea, fatigue, chest pain, and syncope; sudden death can occur. Signs of pulmonary hypertension include prominent a-waves in the jugular venous pulse, a prominent P2 and murmur of tricuspid regurgitation. Introduced in 1964, cardiac catheterization is still required for the clinical assessment. Many patients reveal a vasoconstrictive component in their lung vessels that is potentially reversible therapeutically. Accurate noninvasive diagnostic methods and an understanding of the mechanisms causing pulmonary hypertension are necessary, as is appropriate therapy based upon the results.