OBJECTIVE To analyze the spirometry findings in patients undergoing bone marrow transplant, determining the importance of such findings in predicting postoperative pulmonary complications and looking for correlations with postoperative outcomes. METHODS The spirometry findings in 120 male and female patients, all above the age of 12, were evaluated retrospectively and compared in terms of the following parameters: the type of bone marrow transplant; the underlying disease; cytomegalovirus serology; source of the transplanted cells; smoking; pulmonary infection; history of lung disease; duration of the hematological disease; chemotherapy employed; conditioning regimen; acute or chronic rejection of the transplant; and post-operative mortality. RESULTS In the pre-operative spirometry, 16 patients (13.3%) presented alterations: 6 (5%) presented pure obstruction; 7 (5.8%) presented pure restriction; and 3 (2.5%) presented obstruction accompanied by a reduction in vital capacity. In the post-operative spirometry, 29 patients (24.2%) presented alterations. The chance of presenting post-operative spirometry alterations was greater in patients presenting acute transplant rejection (p = 0.02), patients older than 30 (p = 0.02), female patients (p = 0.02) and patients receiving stem cells (p = 0.01). Having a history of lung disease was found to be associated with greater mortality, as was suffering from chronic transplant rejection. No relationship was found between pre-operative spirometry alterations and post-operative mortality. CONCLUSIONS In bone marrow transplant patients, the alterations found through pre-operative spirometry were not predictive of post-operative pulmonary complications or mortality. Nor were such alterations determinant of whether or not a given patient was a good candidate for bone marrow transplant. Simple spirometry seems to be of little practical importance in the evaluation of such patients.