OBJECTIVE: Insulinoma is a rare pancreatic neuroendocrine tumor that can spontaneously produce excess endogenous insulin, resulting in recurrent and serious hypoglycemia. Patients with insulinoma always have intermittent neuroglycopenia, which has been frequently reported as being misdiagnosed as epilepsy. In this report, we analyzed the clinical data of patients with confirmed insulinoma who had ever been misdiagnosed to have epilepsy. METHODS: The retrospective review was performed on 266 patients with confirmed insulinoma at the First Medical Center of Chinese PLA General Hospital between January 2000 and July 2020. RESULTS: 1. The diagnosis of insulinoma was confirmed in 266 patients. Forty-four patients [male/female=1/1.8, aged (41.25±12.30) years old] were misdiagnosed to have epilepsy, with a misdiagnosis rate of 16.5%. 2. Thirty-eight patients presented with consciousness disorder. Eleven patients presented with palpitation, sweating, and anxiety. Five patients presented with convulsion and 6 patients presented with abnormal behavior and delirium. 3. Twenty-two patients underwent EEG examination. EEG showed spike wave or spike-slow complex wave in 5 patients, decreased α wave and increased slow wave in θ and δ band in 7 patients, and was normal in 10 patients. 4. Thirty-five patients were incorrectly prescribed with AEDs and 22 patients were even misdiagnosed to have refractory epilepsy. 5. All these 44 patients underwent successful surgery, and hypoglycemia symptoms were relieved after insulinoma resection. CONCLUSION: Patients with insulinoma sometimes share common clinical characteristics with epilepsy. To patients with epilepsy or suspected epilepsy, especially with poor response to ADEs, hypoglycemia caused by insulinoma should be emphasized in the differential diagnosis.