Myeloproliferative Neoplasm (MPN), unclassifiable (MPN-U) is a heterogeneous disease with regards to both clinical phenotype and disease course. Patients may initially be asymptomatic or present with leucocytosis or thrombocytosis, anaemia, progressive splenomegaly, constitutional symptom, thromboses or accelerated/blastic phase disease. Treatment strategies are variable and there are no widely accepted consensus management guidelines for MNU-U. Allogeneic Haematopoietic Cell Transplantation (allo-HCT) remains the only curative strategy yet outcomes, to date, are not well defined. We hereby report on the largest retrospective study of patients with MPN-U undergoing allo-HCT, highlighting the potentially curative role and providing clinicians with robust engraftment, GvHD and outcome data to facilitate patient discussion.