Insulinoma is a rare neuroendocrine tumor of the pancreas and is the most common cause of endogenous hyperinsulinemic hypoglycemia. Although 90% of insulinomas are benign tumors, recurrent episodes of hypoglycemia may lead to life-threatening consequences. Since surgery is the only curative method for patients with insulinomas, the preoperative localization of these tumors by appropriate imaging methods is important. In this case series, we report 5 patients with endogenous hyperinsulinemic hypoglycemia, including one with MEN-1 syndrome, who were diagnosed with insulinoma according to the prolonged fasting test. All patients had normal pancreas on upper abdominal magnetic resonance imaging (MRI), therefore, they underwent endoscopic ultrasonography (EUS) for localization of the insulinomas and were operated according to the EUS results. EUS demonstrated well-demarcated tumors in the tail of the pancreas in 4 subjects and in the head of the pancreas in one patient. However, in contrast to EUS results, one patient with MEN-1 syndrome had a glucagonoma and two insulinomas and one patient had not any tumor on histopathological evaluation of the distal pancreas after surgery. In this case series, we aimed to present the diagnostic performance of EUS and the treatment outcomes in a cluster of patients with insulinomas who had not a pancreatic lesion on upper abdominal MRI and to briefly review the currently available imaging methods for localization of insulinomas.