Allogeneic hematopoietic cell transplantation (allo HCT) is the only curative therapy for patients with intermediate-2 or high risk myelofibrosis (MF). We sought to examine the impact of pre-HCT splenomegaly, splenic RT, and marrow fibrosis on overall survival (OS). Subjects with primary or secondary MF who underwent allo HCT using matched related (n=10) or unrelated (n=24) donor grafts, PBSC (n=33) or marrow (n=1), between 2005 and 2021 were identified. Median follow-up was estimated by reverse Kaplan-Meier (KM). Marrow fibrosis regression (defined as any decrease in grade) and GVHD were considered time-varying predictors. Time-to-engraftment and OS were modeled by Cox regression, while post-HCT death rates were estimated via the extended KM method. Logistic regression was used to model fibrosis regression by a specified time point. Our data on engraftment, GVHD, and survival are comparable to that reported by the CIBMTR with this analysis demonstrating a strong correlation between aGVHD, lack of marrow fibrosis regression, and increased risk of death. Novel strategies, such as the use of peri-HCT JAK inhibition and T cell depletion (in-and ex-vivo), may provide rapid marrow remodeling and improve OS in MF patients.