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A 38-year-old male was admitted for profound afebrile leukocytosis 15 days after an uneventful inguinal hernia repair surgery.  The CBC on admission showed hyperleukocytosis (105x 10⁹/L) with left-shifted granulocytes (granulocytes 76%), anemia (Hgb 7.6 g/dL), and thrombocytopenia (52 x 10⁹/L).  His spleen was enlarged. The bone marrow aspirate shows profound left-shifted myeloid hyperplasia (M/E: 15.2), numerous eosinophils and eosinophilic precursors and dyserythropoiesis. Blasts were not increased (1%) (Panel A).  The trephine biopsy showed hypercellularity with increased eosinophils and focal necrosis (Panel B-C). Multiple large, bright-eosinophilic hexagonal or diamond-shaped crystals consistent with Charcot-Leyden crystals were identified (Panel D).  Chronic myeloid leukemia was ruled out with the absence of t(9;22)(BCR::ABL1) by FISH and real-time PCR.   FISH for PDGFRA, PDGFRB, FGFR1, and JAK2 rearrangement revealed the presence of PDGFRB rearrangement in 54% of the leukocytes analyzed.  The final diagnosis of myeloid/lymphoid neoplasm with PDGFRB rearrangement was made. The patient responded to treatment with imatinib. Charcot-Leyden crystals are microscopic crystals composed of eosinophil protein galectin-10 and may be seen in the setting of myeloid neoplasms or other causes of prominent eosinophilia.