Pediatric primary myelofibrosis (PMF) is an extremely rare entity which differs from adult disease in both etiology and outcome.[[1, 2]](https://paperpile.com/c/kO3nmc/v7ZT+LtZX) We report a case of aggressive primary pediatric myelofibrosis driven by somatic trisomy 8, JAK2 and SETBP1 mutations. Disease relapsed +45 days post hematopoietic stem cell transplant. Fortunately, our patient responded to weaning immunosuppression and donor lymphocyte infusion (DLI) and remains in remission with only mild liver and skin graft-versus-host-disease (GVHD). This case is unique not only in its similarity to adult disease but in the response to DLI as salvage therapy.