Spontaneous rupture of the spleen is a rare but important complication in hematological malignancies. Without splenectomy, the mortality rate of these patients is nearly 100%. We present a blastic plasmacytoid dendritic cell neoplasm case with this complication. Nine days after initiation of chemotherapy, the patient had increased epigastric pain and a drop in hemoglobin. CT scan showed an enlarged spleen surrounded by hemorrhage. Spontaneous rupture of the spleen was diagnosed. Although the patient had severe bone marrow suppression due to chemotherapy, emergency splenectomy was performed and the patient recovered.