Pretransplant pulmonary function tests provide baseline data by which to reference subsequent respiratory impairment, as well as important prognostic information, for the hematopoietic cell transplant (HCT) recipient. Abnormalities in forced expiratory volume in 1 second and diffusing capacity of carbon monoxide are associated with early respiratory failure and increased all-cause mortality after allogeneic HCT. These parameters have been incorporated into risk assessment calculators that may aid in clinical decision making. This article discusses the clinical implications of pulmonary function parameters and other risk factors for pulmonary complications in the context of evolving allogeneic HCT practice.