Abstract Background Beckwith-Wiedemann Syndrome (BWS) is a genetic condition characterized by macrosomia, childhood tumors, and neonatal hypoglycemia and hyperinsulinemia. The cause of this hyperinsulinemic hypoglycemia is unknown, but it is believed to be caused by chromosomal mutations at 11p15.5 and genes encoding beta-cell ATP-sensitive potassium channels. In our case, we have an adult patient with a history of BWS who is experiencing hypoglycemia due to a different cause: an insulinoma. This is the first report of insulinoma in an adult with this syndrome. Case Presentation The patient is a 53-year-old male with a history of BWS. Due to shortness of breath, the patient was admitted and discovered to have new and severe systolic heart failure. Patient was started on beta blockers by cardiology. During his hospital stay, he developed hypoglycemia, with glucose levels in the 20s. As the hypoglycemia became more frequent, he was placed on dextrose. Dextrose was turned off to obtain hypoglycemia labs such as insulin, proinsulin, C-peptide, and hydroxybutyrate, but his blood sugar never fell below 80mg/dL. His hypoglycemia was attributed to a beta-blocker side effect or rebound from a dextrose infusion. He was discharged from hospital and sent home. After a loss of consciousness episode at home two weeks later, the patient was readmitted. When he arrived at the emergency department, his blood glucose level was 18mg/dL, and he was given dextrose. After being admitted to the hospital, dextrose was again discontinued, and blood glucose levels dropped to 45mg/dL on serum testing. At the time, C-peptide levels were elevated at 25.7ng/mL, B-hydroxybutyrate levels were 0. 06mmol/L, and insulin levels were above 700uIU/mL. At the time, the choice was between insulin autoantibody syndrome and insulinoma. The patient then had an abdominal computed tomography scan, which revealed a 3.7×2.9cm neuroendocrine tumor in the distal pancreas. Changes in the liver were found to be alarming for metastases, thus an MRI was conducted to confirm this. There was no sign of liver metastases on the MRI. In the interim, the patient was started on subcutaneous octreotide 50 mcg twice daily. Given the patient's underlying heart problems, diazoxide was not pursued. Octreotide was increased to 100mcg subcutaneously three times daily throughout his hospital stay, and he was discharged home with a continuous glucose monitor and intentions to operate later that month. Conclusions Although BWS has been linked to a higher risk of childhood malignancies, it's uncertain whether BWS could be a predisposing factor for the development of insulinoma. Because this is such a rare disorder, there is a paucity of information on predisposition or risk factors. However, the link between macrosomia and tumor growth in BWS suggests that there may be a predisposition to insulinoma that has yet to be investigated. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.