Controversy has surrounded the use of single-lung transplantation (SLT) for the treatment of endstage obstructive lung disease. In recent years, several transplant centers have performed SLT for such indications. In this report, we describe functional results in patients undergoing SLT for obstructive lung disease, twenty-two followed over one year and 10 over two years. Data include pulmonary function testing, gas exchange, quantitative ventilation and perfusion to the lung graft, and results of symptom-limited graded cycle exercise testing after SLT. Our results show improvement in obstructive dysfunction FEV1 0.49 +/- 0.13 L (16 +/- 4% predicted) pre-SLT to 1.71 +/- 0.43 L (57 +/- 12% predicted) 3 mo after SLT, FEV1/FVC 0.30 +/- 0.07 pre-SLT to 0.75 +/- 0.09 3 mo after SLT, and improvement in arterial oxygenation, PaO2 58 +/- 10 mm Hg pre SLT to PaO2 86 +/- 13 mm Hg 3 mo post-SLT. In addition, these improvements were sustained up to 1 to 2 yr post-SLT. The majority of ventilation and perfusion go to the new lung graft. After SLT, patients have reduced maximum oxygen consumption (VO2max 40 to 60% predicted) but do not have ventilatory limitation to exercise and can carry out daily activities without compromise. We conclude that SLT is a viable medium-term therapeutic option for endstage obstructive lung disease. The long-term future of this technique remains to be determined.