A previously healthy 2-year-old girl had fever and cough for 2 days. Peripheral blood showed marked leukocytosis (white blood cells, 75 000/μL) with 76% blasts (panels A-D). The blasts were medium to large size with scant agranular pale-blue cytoplasm. The nuclei were irregular, folded, or flowerlike. Some had a prominent nucleolus. Cerebrospinal fluid analysis showed 87% blasts (panels F-H). The patient's serum lactate dehydrogenase was 3759 IU/L. She had extensive lymphadenopathy without skin lesion or hepatosplenomegaly. By flow cytometry, the blasts were positive for CD4, CD7, CD36, CD38, dim CD45, CD123, and HLA-DR and negative for tested lineage markers CD2, CD3 (surface and cytoplasmic), CD5, CD14, CD19, CD20, CD33, CD34, CD41, CD56, CD64, CD117, TdT, and myeloperoxidase (panel I). By immunohistochemistry, the blasts were positive for T-cell leukemia 1 (panel E). Karyotyping was complex: 47, X, der(X)t(X;8)(q24;q24.1), add(5)(p13), −6, del(6)(q13q27), +8, der(8), t(X;8), add(8)(q24.1)×2, del(9)(q12q31), del(9)(q13q22), der(10;13)(q10;q10), add(12)(p13), −14, +3mar[20]. Fluorescence in situ hybridization (FISH) confirmed MYC rearrangement t(X;8)(q24;q24.1). FISH was positive for single-copy deletion of the ETV6 gene and negative for MLL gene rearrangement, BCR/ ABL1, and ETV6/ RUNX1 translocation.The patient was diagnosed with blastic plasmacytoid dendritic cell neoplasm and was in complete remission by bone marrow biopsy 4 weeks after initial high-risk acute lymphoblastic leukemia therapy. This case has the following unique features: young age, negative CD56, acute leukemia without skin lesion, and involvement of the central nervous system.