Background: There is signifi cant heterogeneity within the primary graft dysfunction (PGD) syndrome. We aimed to identify distinct grade 3 PGD phenotypes based on severity of lung dysfunction and patterns of resolution. Methods: Subjects from the Lung Transplant Outcomes Group (LTOG) cohort study with grade 3 PGD within 72 h after transplantation were included. Latent class analysis (LCA) was used to statistically identify classes based on changes in PGD International Society for Heart & Lung Transplantation grade over time. Construct validity of the classes was assessed by testing for divergence of recipient, donor, and operative characteristics between classes. Predictive validity was assessed using time to death. Results: Of 1,255 subjects, 361 had grade 3 PGD within the fi rst 72 h after transplantation. LCA identifi ed three distinct phenotypes: (1) severe persistent dysfunction (class 1), (2) complete resolution of dysfunction within 72 h (class 2), and (3) attenuation, without complete resolution within 72 h (class 3). Increased use of cardiopulmonary bypass, greater RBC transfusion, and higher mean pulmonary artery pressure were associated with persistent PGD (class 1). Subjects in class 1 also had the greatest risk of death (hazard ratio, 2.39; 95% CI, 1.57-3.63; P < .001). Conclusions: There are distinct phenotypes of resolution of dysfunction within the severe PGD syndrome. Subjects with early resolution may represent a different mechanism of lung pathology, such as resolving pulmonary edema, whereas those with persistent PGD may represent a more severe phenotype. Future studies aimed at PGD mechanism or treatment may focus on phenotypes based on resolution of graft dysfunction. © 2013 American College of Chest Physicians.