Background: Allogeneic hematopoietic cell transplant (allo-HCT) remains the only potentially curative therapeutic modality for patients with primary or secondary myelofibrosis (MF). However, many patients (pts) are ineligible for allo-HCT and transplant-related mortality can be substantial. Data on the efficacy and safety of allo-HCT are mixed and largely derived from retrospective studies. Methods: To synthesize the available evidence, we conducted a systematic review and meta-analysis searching Cochrane Library, Google Scholar, Ovid Medline, Ovid Embase, PubMed, Scopus, and Web of Science Core Collection from inception to October 11, 2020 for studies on allo-HCT in MF. Databases were searched using a combination of controlled vocabulary and free text terms for relevant studies on the efficacy and safety of allo-HCT in pts with primary and secondary MF. This study protocol has been registered on PROSPERO (CRD42020188706). Random-effects models were used to pool response rates for the co-primary outcomes of 1-year, 2-year and 5-year overall survival (OS). Results: We identified 4247 studies after duplicate removal. 393 studies were assessed as full-texts for eligibility and 43 studies (38 retrospective, 1 prospective study, 4 phase II clinical trials) with 8739 pts were included in this meta-analysis. Study quality was limited by the absence of randomized clinical trials and retrospective design of most studies. Rates of 1-year, 2-year, and 5-year OS were 66.7% (95% confidence interval: 63.5-69.8%), 64.4% (57.6-70.6%), and 55.0% (51.8-58.3%), respectively. Rates of 1-year, 2-year, and 5-year non-relapse mortality were 25.9% (23.3-28.7%), 29.7% (24.5-35.4%), and 30.5% (25.9-35.5%), respectively. Among evaluable studies, rates of 1-year, 2-year, and 5-year relapse-free survival were 65.3% (56.5-73.1%), 56.2% (41.6-69.8%), and 53.6% (39.9-66.9%), respectively. Adverse events related to all-HCT were manageable with rates of acute and chronic graft-versus-host disease in 44.0% (39.6-48.4%; grade III/IV: 15.2%) and 46.5% of patients (42.2-50.8%; extensive or moderate/severe: 26.1%), respectively. Subgroup analyses did not show any significant difference between conditioning regimen intensity (myeloablative vs reduced-intensity), median patient age, and proportion of DIPSS-intermediate-2/high pts. Conclusions: Given the poor prognosis of patients not receiving transplant and in the absence of curative non-transplant therapies, our results support consideration of allo-HCT for eligible pts with MF. However, additional studies in pre- and post-allo-HCT setting are necessary to enhance patient selection (e.g. by incorporation of molecular markers), to optimize transplant strategies (e.g. peri-transplant ruxolitinib, conditioning regimens, and donor selection), symptom management and decrease non-relapse mortality.