Introduction: A U-500R Insulin Program was implemented for patients requiring >200 units of insulin. Similar to U-100 insulin, titration was based on patient BG logs. However, there was concern for nocturnal hypoglycemia, as U-500R is expected to peak while the patient is sleeping and s/he may not realize hypoglycemia is occurring. In this report, we describe how continuous blood glucose monitoring (CGM) may have prevented serious hypoglycemia in a patient receiving U-500R insulin. Case study: A 61 year-old patient was receiving U-500R. His BG log demonstrated an average: FBG of 220 mg/dL, breakfast PPBG of 209 mg/dL, lunch PPBG of 181 mg/dL, dinner PPBG of 154 mg/dL and bedtime BG of 155 mg/dL, with no values <70 mg/dL. Based on these readings, the evening dose was increased to 0.29 mL (145 units) and the morning dose remained at 0.37 mL (185 units). A two-week CGM was then implanted into the patient’s arm. Despite the lack of patient reported hypoglycemic episodes or evidence of hypoglycemia per BG logs, the patient was having nocturnal hypoglycemic episodes between midnight and 6 am where his BG was below 70 mg/dL13% of the time, with a couple of readings dropping below 50 mg/dL and one reading reaching 40 mg/dL. The dose was adjusted and repeated CGM was used to more accurately stabilize his dose. Conclusion: Had this patient’s U-500R dose been adjusted based on BG values, and not CGM, we likely would have continued to increase the nighttime dose to reduce FBG values, which may have resulted in severe hypoglycemia or death. Disclosures: The authors have declared no potential conflicts of interest.