Objective:We report a case of unilateral adrenal hemorrhage resulting in adrenal insufficiency in a patient on rivaroxaban for thromboprophylaxis after total knee arthroplasty.Methods: The clinical presentation, laboratory findings, and outcome of the case are described. An overview of the etiology, diagnosis, and treatment of adrenal hemorrhage is reviewed.Results: A 61-year-old male underwent bilateral total knee replacements and postoperatively was started on rivaroxaban at 10 mg daily for thromboprophylaxis. About 2 weeks after the procedure, the patient presented with abdominal pain, nausea, vomiting, and generalized weakness. Abdominal computed tomography scan identified an ill-defined heterogeneous density in the left suprarenal fossa, and an abdominal magnetic resonance imaging scan identified diffuse thickening of the left adrenal gland with periadrenal fat stranding suggestive of adrenal hemorrhage. Adrenal insufficiency was suspected and confirmed with a cosyntropin stimulation test. Pre-stimulus cortisol level was 2.7 µg/dL and 60 minutes after cosyntropin administration it was 2.5 µg/dL. The patient was started on intravenous hydrocortisone at 100 mg every 6 hours with improvement of symptoms and discharged on oral hydrocortisone at 20 mg twice daily. Follow up abdominal magnetic resonance imaging 6 weeks after discharge demonstrated resolution of the left adrenal hemorrhage.Conclusion: A high clinical suspicion and early detection of adrenal hemorrhage in a patient on anticoagulation can allow for earlier intervention and improved outcomes. (AACE Clinical Case Rep. 2019;5:e70-e72) Abbreviations: CT = computed tomography; MRI = magnetic resonance imaging