The panel chose PAH as the topic of this guideline, adopting the nomenclature developed at the 1998 World Health Organization International Conference and recently updated at the Third World International Conference in 2003. In so doing, the panel broadened the topic compared with the consensus statement on PPH 10 years earlier, but excluded other causes of pulmonary hypertension from their analysis, including chronic parenchymal or airways disease and left-sided heart disease. Although there is no uniformly accepted definition for PAH, we recognize and adopt the hemodynamic definition developed by the National Institutes of Health Registry on Primary Pulmonary Hypertension, which has been widely used in subsequent clinical trials: a mean pulmonary artery pressure ≥ 25 mm Hg, with a pulmonary capillary wedge pressure ≤ 15 mm Hg, both measured at rest by right-heart catheterization. While the panel is unable to provide specific, evidence-based guidelines addressing thresholds for the timing of diagnostic and therapeutic interventions in suspected or proven PAH, respectively, we wish to emphasize that PAH is a serious and frequently life-threatening condition that should be approached aggressively once its presence is suspected. The panel chose the following topics for review and analysis, based on the consensus impression that these topics were clinically important and had sufficient evidence to support recommendations: (1) screening, early detection, and diagnosis; (2) medical therapies; (3) surgical therapies; (4) sleep-disordered breathing; and (5) prognosis.