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Bronchiolitis obliterans, defined histologically or clinically, is the most significant long-term cause of morbidity and mortality after lung transplantation. It shares many pathogenetic features with chronic allograft dysfunction that can occur in bone marrow, liver, heart, and kidney recipients. Lessons learned in the prevention and management of this disorder in lung recipients therefore should have application to the analogous process that develops in other organ allograft recipients. Because the lung is exposed to the external environment, it can be sampled repeatedly by techniques like bronchoalveolar lavage and transbronchial lung biopsy with little or no long-term adverse consequence to the allograft. Excellent pulmonary function tests also are available with which to assess the functional capacity of the allograft and to correlate with the results from immunologic testing. For these reasons, this disorder in lung recipients could serve as a model to determine the pathogenesis and treatment of the analogous disorder that may develop in other major organ recipients. Because this disorder most likely is immunologic in origin, advances in transplant immunology that create tolerance between the donor and recipient as well as efforts to prevent CMV infection and airway ischemic injury likely will be effective preventive measures. Although augmented immunosuppression appears to be of some benefit in treating bronchiolitis obliterans, it is far from optimal and new or better use of current immunosuppressive medications is warranted. Because the number of recipients at any one center is too few to critically assess the efficacy and safety of different immunosuppressive regimens, it is likely that collaboration between transplant centers will be necessary for success to be achieved.