Allogeneic hematopoietic cell transplantation (allo-HCT) remains the sole curative option for myelofibrosis (MF). Relapse remains a significant problem, however, occurring in up to 20% to 30% of cases. Donor lymphocyte infusion (DLI) represents a potentially effective strategy for relapse prevention and management, but the optimal timing based on measurable residual disease/chimerism analyses and the choice of regimen remain undetermined. We performed a retrospective real-world analysis of a multicenter cohort of MF allo-HCT recipients from 8 European transplantation centers who received DLI between 2005 and 2022. Response was assessed using International Working Group-Myeloproliferative Neoplasms Research and Treatment-defined response criteria, and survival endpoints were estimated using the Kaplan-Meier estimator and log-rank test. The study included 28 patients with a median age of 58 years and a Karnofsky Performance Status of >80. The majority of patients had Dynamic International Prognostic Scoring System-plus intermediate-2 or high-risk disease at the time of allo-HCT. In vivo T cell depletion was used in 20 patients (71.2%), with 19 of the 20 receiving antithymocyte globulin. The indication for DLI was either "preemptive" (n = 15), due to a decrease in recipient chimerism (n = 13) or molecular relapse (n = 2), or "therapeutic" (n = 13) for clinician-defined hematologic/clinical relapse. No patient received DLI prophylactically. The median time of DLI administration was 23.4 months post allo-HCT. Of the 16 patients receiving multiple DLIs, 12 were part of a planned escalating dose regimen. The median follow-up from the time of first DLI was 55.4 months. The responses to DLI were complete response in 9 patients, partial response in 1 patient, and clinical improvement in 6 patients. Chimerism levels improved in 16 patients, and stable disease was reported in 5 patients. No response or progression was reported in 7 patients. DLI-induced acute graft-versus-host disease (aGVHD) was reported in 11 patients (39%), with grade III-IV aGVHD in 7 (25%). The median overall survival from the time of first DLI was 62.6 months, and the cumulative incidence of relapse/progression after first DLI was 30.8% at 6 months. This study highlights that good response rates can be achieved with DLI even after frank relapse in some patients in a cohort in which other treatment options are very limited. More prospective studies are warranted to identify the optimal DLI regimen and timing to improve patient outcomes.