INTRODUCTION: Babesiosis is a zoonotic disease caused by obligate intracellular protozoa that reproduce in erythrocytes. We present a case of transfusion-transmitted babesiosis (TTB) leading to acute liver failure (ALF). Whereas mild liver chemistry abnormalities are common in babesiosis, to the authors’ knowledge this is the first case of TTB directly leading to ALF. CASE DESCRIPTION/METHODS: A 79-year-old man from New Jersey with end stage renal disease presented with two weeks of flu-like illness and was found to have profound liver function abnormalities consistent with ALF. Six weeks prior the patient was hospitalized for a diverticular bleed at which time he received multiple packed red blood cell transfusions and recovered to his baseline health. At that time, liver chemistries were normal. On arrival, he was afebrile and normotensive. He was oriented but lethargic. Skin exam notable for pallor. His abdomen was benign. Initial investigations revealed AST 3497 IU/L, ALT 2719 IU/L, ALP 259 IU/L, TB 5.2mg/dl, DB 3.6mg/dl. INR was 4.1, Hgb 8.7g/dL, and fibrinogen 252mg/dl. LDH 2003 IU/L with haptoglobin < 8.0mg/dl. Peripheral smear revealed ring-shaped intra-erythrocytic trophozoites (Figure 1). Babesia microti PCR was positive. Atovaquone and azithromycin were started and exchange transfusion performed. Fevers and worsening encephalopathy progressed despite directed treatment. Multi-system organ failure developed and care was withdrawn. Further testing determined our patient was a recipient of babesia microti contaminated transfusion. DISCUSSION: Babesiosis is a world-wide emerging disease caused by intra-erythrocytic protozoa that are transmitted primarily through Ixodes ticks but also through blood transfusion. TTB is often severe in presentation with a mortality rate of approximately 20%. Marked hemolytic anemia, disseminated intravascular coagulation, and adult respiratory distress syndrome may develop. Case series have established that patients with babesiosis exhibit abnormal liver chemistries with median values notable for ALT of 59 IU/L and AST 79 IU/L. A literature review reveals just one published case of babesiosis presenting as ALF, and no such cases when babesia is transmitted through transfusion. Babesiosis should be considered in the differential diagnosis of ALF in patients living in or having recently travelled to an endemic area or who have recently received transfusions. In such patients, we recommend performing blood smear to prevent delay in treatment.