Gastrointestinal involvement is a rare manifestation of Acute Myeloid Leukemia (AML). We present a case of a 76-year old African American female with a past medical history of hypertension and chronic kidney disease (baseline creatinine of 1.3 mg/dL) who presented to the emergency department with chief complaint of voluminous, watery diarrhea over the course of five days. The diarrhea was frequent, occurring more than 10 times per 24 hour period, large volume, watery, non-bloody, and with nocturnal symptoms. There was no association between her diarrhea with oral intake. She also had symptoms of lethargy and shortness of breath. Upon presentation her vital signs were significant for a fever of 101F orally, HR 141 bpm, BP 105/59 mmHg. Her physical examination was significant for tachycardia without murmurs. Lungs were clear to auscultation. Abdominal examination revealed a soft abdomen, non-tender to palpation with hyperactive bowel sounds, no rebound or guarding. Non-contrast CT scan of her head, chest, abdomen, and pelvis showed no signs of bowel wall thickening, however, the liver was enlarged to 22cm in craniocaudal length. Initial laboratory evaluation revealed the patient to have acute on chronic renal failure with a creatinine of 3.3 mg/dL, bicarbonate 10 mEq/L, uric acid 11 mg/dL, phosphorous 5.4 mg/dL, and a white blood cell count of 126,000 of which 78% were blasts. Stool studies were unremarkable. In the emergency department her mental status deteriorated and she became increasingly lethargic and hypotensive. She was diagnosed with acute blast crisis of Acute Myeloid Leukemia (AML) and Tumor Lysis Syndrome (TLS) and was transferred to the Intensive Care Unit on vasopressor medications. Her hospital course was complicated, secondary to her overwhelming disease which, on autopsy, was confirmed to have invaded nearly every tissue in her body including her liver, colon, and small intestine (images 1-3). We found this case interesting because of the unique presentation of diarrhea and the multi-organ system involvement of this stereotypically hematological disease. Gastrointestinal involvement is not a frequent initial manifestation of AML. When involved, the mouth, rectum, and anal canal are the most commonly affected sites that lead to patient symptoms. This patient's voluminous diarrhea prompting medical evaluation was secondary to the leukemic invasion of the small intestine and colon.Figure 1Figure 2Figure 3