Some studies on the predictive value of determining pulmonary function prior to allogeneic hematopoietic cell transplantation (allo-HCT) have shown a significant association between pulmonary function test (PFT) parameters and pulmonary complications, and mortality. However, the percentage of patients showing abnormalities in pretransplant PFT parameters is low. We comprehensively evaluated the effect of pretransplant PFT parameters, including a marker of small airway disease (ratio of the airflow rate of 50% vital capacity to the airflow rate of 25% vital capacity (V˙50/V˙25), on outcomes in 206 evaluable patients who underwent allo-HCT at our institute. Notable among the significant parameters in a univariable analysis, V˙50/V˙25 was the most powerful indicator of survival following allo-HCT (delta-Akaike information criterion [∆AIC]=12.47, ∆chi(2) =14.47; P= 0.0001). Additionally, a pretransplant lung function score (pLFS) established by applying three parameters with superior predictive values including V˙50/V˙25 represented a better discriminating variable for the prediction of survival. Our data demonstrate that a pLFS incorporating a parameter of small airway disease, rather than the parameters of central airway obstruction, may be useful for predicting patient survival following allo-HCT.