Single lung transplantation has been advocated as a definitive treatment for primary pulmonary hypertension. Because of reports of improved survival in some patients with vasodilators and anticoagulants, the timing of referral for single lung transplantation needs to be examined. Survival in primary pulmonary hypertension was estimated, with the use of a proportional hazards model, from data obtained from the National Institutes of Health registry on primary pulmonary hypertension. Waiting times for single lung transplantation, obtained from the United Network for Organ Sharing, were found to follow an exponential distribution. Under the assumption that waiting time and survival are independent, a model was developed to estimate the probability of surviving to single lung transplantation, depending on the waiting time for a single lung transplantation, and the delay in transplant referral. Examples were computed with hemodynamic data from the National Institutes of Health registry on primary pulmonary hypertension: waiting times of 6, 12, 18, and 24 months and delays in single lung transplantation referral of 0, 1, 2, and 3 years. For a waiting time of 6 months, the chance of surviving to single lung transplantation with a 3-year delay varies from 19% for a patient with a mean pulmonary artery pressure of 80 mm Hg to 72% for a patient with a mean pulmonary artery pressure of 41 mm Hg. For a waiting time of 24 months and a 3-year delay in single lung transplantation referral, this probability varies from 14% (mean pulmonary artery pressure 80 mm Hg) to 59% (mean pulmonary artery pressure 41 mm Hg). Patients with primary pulmonary hypertension should be evaluated for their acute response to vasodilators. In patients who do not respond, the timing of referral for single lung transplantation should be influenced by the patient's estimated survival without single lung transplantation and their chance of surviving and receiving a single lung transplantation, depending on the delay in transplantation referral
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