Based on the experience to date with prognostic models for predicting the natural history of various lung diseases, there is every reason to be skeptical about the validity of the lung allocation model. Space limitations preclude a full review of the literature for each disease; CF will be discussed as an example. Analyzing a cohort of 673 CF patients from the Hospital for Sick Children in Toronto, Kerem and colleagues31published a landmark study in 1992 that identified FEV1 as the single most significant predictor of mortality. These investigators noted that an FEV1 of < 30% predicted was associated with a 2-year mortality rate of 50%, and they suggested using this FEV1 value as a threshold for lung transplant referral, a recommendation that was subsequently incorporated into published international guidelines for the selection of lung transplant candidates.32 Other single-center studies33–34 that followed offered discrepant findings, with median survival times of 3.9 to 4.6 years associated with an FEV1 of < 30%. In 2001, Liou and colleagues35 published a 5-year survivorship model that was derived from data on 5,800 patients in the multicenter Cystic Fibrosis Foundation Patient Registry and validated using data from an additional 5,800 registry patients. Nine parameters, including FEV1, were identified as independent predictors of mortality by multivariate analysis and were incorporated into the model. When applied to the validation cohort, this complex model performed in a superior fashion to the simpler model proposed by Kerem et al,31 utilizing FEV1 alone. More recently, Mayer-Hamblett and colleagues,36 developed and validated a 2-year mortality model utilizing methods identical to those of Liou et al35in conjunction with a more current and larger cohort of patients (n = 14,572) from the Cystic Fibrosis Foundation Patient Registry.36 In contrast to the findings of Liou et al,35“this well-fitting model derived from the largest collection of data available on patients with CF provided no better diagnostic accuracy than the simpler FEV1 criterion.”36 Both the multivariate model and the FEV1 alone were far better at identifying patients who would survive for 2 years than those who would die. Given the conflicting data generated by these studies, are we not justified in questioning the ability of the new lung allocation model, which was derived from a smaller cohort of CF patients and lacks validation, to predict mortality?