A 7-year-old girl was admitted to Xiangya Hospital due to systemic lymphadenectasis for 2 months and skin ecchymosis for 3 days. Nine months ago, the girl experienced painless nodules in the left lower extremity with no apparent causes. Three months later, dermatorrhagia and ecchymosis occurred in many regions such as the periocular areas, conjunctiva, oral mucosa, perineal area, and groin, with a "raccoon sign" in both eyes; superficial lymphadenectasis and hepatosplenomegaly were also observed in many regions. The pathological sections for the skin nodules showed malignant tumors in lymphohematopoietic cells, and in combination with clinical manifestations, immunohistochemistry, and positive results for CD4, CD56, and CD123 by bone marrow flow cytometry, the girl was diagnosed with blastic plasmacytoid dendritic cell neoplasm. Then high-risk ALL regimen was applied as the chemotherapy for this girl. At present, the girl has been followed up for 3 months; ecchymosis has disappeared, and the enlarged lymph nodes have shrunk. No abnormal cells have been found in bone marrow morphological examination, and bone marrow flow cytometry has shown that primitive precursor cells account for 1.5% and express CD33, CD34, CD123, and CD117.