Pretransplant pulmonary function tests (PFTs) have been checked mostly in myeloablative allogeneic stem cell transplantation (Allo-SCT). Their value in the setting of reduced intensity conditioning Allo-SCT (Allo-RIC) has been less explored. We retrospectively evaluated the predictive value of PFTs on posttransplant pulmonary complications (PPC) and outcomes in 195 consecutive Allo-RIC patients, based on fludarabine plus busulphan or melphalan. PFT parameters included forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), FEV1/FVC ratio, total lung capacity (TLC), residual volume, and diffusion capacity for carbon monoxide (DLCo) corrected for the hemoglobin levels. Pretransplant PFTs abnormalities were observed in 130 patients (66%). The most frequent abnormalities were abnormal DLCO (n = 83, 44%), followed by FEV1/FVC (n = 75, 38%) and FVC (n = 47, 24%). The abnormalities were severe in 25 (13%) patients, moderate in 65 (33%) and mild in 40 patients (21%). Multivariate analysis showed that TLC was significantly associated with PPC, nonrelapse mortality and overall survival (OS), (HR 4.2, 95% CI. 2-8.5; HR 3.8, 95% CI. 1.7-8.5; HR 2.3, 95% CI. 1.3-4.1, respectively, P = 0.01), while abnormal FVC had a negative impact on PPC and OS (HR 1.8, 95% CI. 0.98-3.6, P = 0.06 and HR 1.7, 95% CI. 1.1-2.6, P = 0.008). This study emphasizes the valuable role of PFTs in identifying patients at risk for PPC, NRM, and lower OS in the Allo-RIC setting.