Although we have not yet obtained the survival results that have been observed in heart and renal transplantation, the survival rate in lung transplantation is improving. Because the lung is the only organ that is continuously exposed to the environment after transplantation, infection continues to be the major cause of early and late morbidity and mortality. Bronchiolitis obliterans, the second most common cause of late morbidity and mortality, is a progressive and currently untreatable condition resulting in lung dysfunction. The cause of this condition after transplantation is likely multifactorial and related to processes that result in allograft lung injury, such as rejection, bacterial infection, and cytomegalovirus infection. Future improvement in intermediate and long-term survival after lung transplantation will largely depend on prevention and long-term control of infection and subclinical rejection.