This is a 74-year-old male with a history of AML with myelodysplasia who presented with sinusitis. The sinus contents showed dense mononuclear infiltrate disrupting the normal sinus mucosal glands. The infiltrative cells were atypical with irregular nuclear borders, high nuclear to cytoplasmic ratio, and an open chromatin pattern. The cytoplasm was eosinophilic and slightly granular. These cells were positive for MPO and negative for cytokeratin consistent with myeloid sarcoma.