Rationale: In 2005, lung allocation for transplantation in the United States changed from a system based on waiting time to a system based on the Lung Allocation Score (LAS). Objectives: To study the effect of the LAS on lung transplantation for idiopathic pulmonary arterial hypertension (IPAH) compared to other major diagnoses. Methods: We studied 7,952 adults listed for lung transplantation between 2002 and 2008. Analyses were restricted to patients with IPAH, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF). Transplantation, waiting list mortality, and posttransplant mortality were compared between diagnoses for patients listed before and after implementation of the LAS. Measurements and Main Results: Likelihood of transplantation from the waiting list increased for all diagnoses after implementation of the LAS. Waiting list mortality decreased for every diagnosis, except for IPAH, which remained unchanged. Implementation of the LAS was not associated with changes in posttransplant mortality for any diagnosis. Under the LAS system, patients with IPAH were less likely to be transplanted than patients with IPF (HR, 0.53; p<0.001) or CF (HR 0.49; p<0.001) and at greater risk of death on the waiting list than patients with COPD (HR, 3.09; p<0.001) or CF (HR, 1.83; p=0.025) after adjustment for demographics and transplant type. Posttransplant mortality for IPAH was not statistically different from that of other diagnoses. Conclusions: Implementation of the LAS has improved the likelihood of lung transplantation for listed patients with IPAH, but mortality on the waiting list remains high compared to other major diagnoses.