Pulmonary function testing (PFT) is used to characterize non-infectious pulmonary complications after allogeneic BMT. Identifying high-risk patients could facilitate preventive or early therapeutic measures. The objectives of the study were first, to review available data on PFT changes after BMT and second, to validate a previously published predictive index for PFT obstruction in patients transplanted at one center. For the systematic review, frequency, severity and time course of PFT changes after BMT and for the validation study, retrospective cohort comparing predicted with observed PFT, and calculation of indices of predictive accuracy were summarized. The validation study involved 434 patients from Princess Margaret Hospital, Toronto, Canada, who received their first BMT between 1980 and 1997, survived for at least 6 months and had adequate PFT follow-up. The systematic review included 20 studies. After BMT, decreased diffusion and total lung capacity were common and partially reversible. Obstruction was less common. The validation study of a previously published index, performed in 434 patients, found a sensitivity and specificity of 48% and 68% for identifying patients who develop obstruction. We concluded that PFT changes after BMT are common. A published predictive index is not sufficiently accurate to identify high-risk patients for potential preventive or early therapeutic strategies.