Aim. Pulmonary function tests (PFT) have an important role in the assessment of pulmonary and nonpulmonary complications of hematopoetic stem cell transplantation (HSCT). In this study the relationship between PFTs and DLCOadj values and the complications of HSCT was investigated. The possible role of iron overload in the deterioration of the PFTs after HSCT was also searched. Methods. One hundred and fifty one patients who had undergone allogeneic HSCT between years 2003 through 2008, and had the records of PFTs prior to and at 1, 3, 6, 9 and 12 months after transplantation were included in the study. Prospectively collected data of these patients were analysed retrospectively. Results. Although no significant difference was identified in other PFT parameters, a significant decrease in DLCOadj was determined after 1st and 3rd months of HSCT. A significant correlation was found between pretransplant DLCOadj value <%70 and sinusoidal obstruction syndrome (SOS) (P=0.001, r=0.323), but in multivariate analysis pretransplant DLCOadj was not an independent predictor of SOS; only total body irradiation (TBI) (OR: 3.673, %95 CI: 0.880-15.804), the day of platelet engraftment (OR=1.093, %95 CI: 1.029-1.161) and serum ferritin (OR=L001, %95 CI: 1.000-1.001) were significant. Advancing age and serum ferritin levels >600 ng/mL were the independent risk factors for pretransplant DLCOadj <%70 (OR: 0.970, %95 CI: 0.941-0.999 and OR: 2.355, %95 CI: 1.058-5.241 respectively). Conclusion. Although a significant correlation exists between pretransplant DLCOadj values and post-transplant SOS development, pretransplant DLCOadj was not an independent predictor of SOS. Increased serum ferritin levels were common both for pretransplant DLCO decrease and post-transplant SOS development. Iron induced endothelial damage may be the common pathophysiologic mechanism causing lung and liver vulnerability, and DLCOadj may be a non-invasive method of demonstrating this vulnerability.