Here we report an unusual patient, who was a previously healthy 4-yr-old female, and presented with 2 wk of leg pain and fever.Peripheral blood count revealed white blood cells (WBC) 85.8 K/uL, Hgb 9.4 g/dL, and platelets 56 K/uL.Peripheral blood flow cytometry showed approx. 16% monocytes and 15% blasts (CD45 dim+, CD34+, CD117+, CD33+, CD38+, CD13+, CD11c+, CD64 partial+, HLADR+, and CD4 dim+, MPO-).A bone marrow biopsy revealed hypercellularity with myeloid predominance and 11% myeloblasts.A diagnosis of JMML (based on the 4th WHO classification) was favored, given increased blasts, monocytosis, and neg. FISH studies for BCR::ABL1.Cytogenetics showed abnormal karyotypes with trisomy 6.Next-generation sequencing (NGS) identified NUP98::NSD1 fusion and KRAS G12D mutation (c.35G>A, 28.2% variant allele fraction [VAF]).The patient received chemotherapy (fludarabine, cytarabine, and azacitidine), with 5.7% minimal residual disease (MRD) by flow cytometry after three cycles of chemotherapy.Then the patient received a bone marrow transplant (BMT) with busulfan, cyclophosphamide, and melphalan conditioning regimen.Six cycles of azacitidine maintenance were started on Day 165 postBMT, and the patient remains in complete remission 2 years after transplant.In summary, it is′ critical to recognize these unusual features of JMML in practice and further risk stratify JMML, especially because rare JMML-like disease may self-resolve, and a significant percentage of JMML relapse after BMT.