A consensus panel convened by the American College of Chest Physicians developed guidelines for the treatment of pulmonary arterial hypertension (PAH) that were published in 2004. Subsequently, several important clinical trials have been published, and new treatments have received regulatory approval. In addition, add-on and combination therapy are being explored, which promise to open new therapeutic avenues. This article, taking into consideration studies published prior to September 1, 2006, provides an update to the previously published guidelines. The original guidelines have been summarized, a discussion of new studies has been added, and the treatment algorithm has been revised to take into account recent developments in therapy. This update provides evidence-based treatment recommendations for physicians involved in the care of patients with PAH. Due to the complexity of the diagnostic evaluation required and the treatment options available, referral of patients with PAH to a specialized center continues to be strongly recommended.