Insulinoma is a rare and potentially life-threatening tumor if not treated promptly. The time from initial presentation to diagnosis may be prolonged in patients who have impaired awareness of hypoglycemia. A 34-year-old female with daytime hypoglycemia awareness and nocturnal hypoglycemia unawareness was initially treated for reactive hypoglycemia until continuous glucose monitoring (CGM) data revealed nocturnal hypoglycemia. Outpatient CGM was used to help establish the diagnosis of insulinoma and to help expedite treatment. Given the potential for hypoglycemia unawareness in patients with life-threatening causes of hypoglycemia and given the potential for missed diagnosis in these patients, CGM should be considered as an adjunctive diagnostic tool in all patients presenting for hypoglycemia evaluation.