The development of pulmonary complications after hematopoietic stem cell transplantation is responsible for significant morbidity and mortality. The incidence of pulmonary disease has been reported to be as high as 50% of all patients that undergo transplant. The most common manifestation of early onset lung disease is idiopathic pneumonia syndrome. This can occur in autologous and allogeneic transplants, with an incidence between 5% and 10% and a mortality rate as high as 74%(1). Late onset pulmonary disease may be even more frequent and has been reported between 10-24% in recipients of allogeneic HSCT(2-4). Additionally, a recent study demonstrated 26% of patients develop airflow obstruction after transplant and this was correlated with mortality(5). One quite useful classification system divides late onset pulmonary disease into bronchiolitis obliterans and interstitial pneumonia(4). Interstitial pneumonia is a condition characterized by diffuse infiltrates, often with lymphocyte predominance, and associated with restrictive defects on pulmonary function testing. Bronchiolitis obliterans is characterized by progressive airflow obstruction and a normal radiograph (except possibly associated air trapping). The incidence of bronchiolitis obliterans after HSCT varies widely, but is usually reported to be between 1% and 11%(6-8), although the presence of post HSCT obstructive airway disease was reported at 26% in a recent large study(5). Late onset pulmonary diseases are often treated with increased immunosuppression, but the prognosis is poor with limited response to therapy(9; 4).