Insulinomas are very rare tumors. Diagnosis of insulinoma is often delayed or misdiagnosed because of its various symptoms. We report a patient with hypoglycemic encephalopathy who had repetitive behavior changes, diagnosed as a pancreatic insulinoma. A 52 years old man was referred to a memory and dementia clinic for evaluation of his repetitive abnormal behavior changes. He has threatened his wife with violent acts and showed aggressive behaviors, but he couldn't remember when he was recovered to normal state. During the hospitalization, we noticed that his repetitive abnormal behaviors were correlated to severe hypoglycemia. After we corrected glucose level, his symptoms were disappeared. We performed an abdomen-pelvis CT scan, revealing pancreatic head tumor. After he took surgical treatment, His symptoms were fully recovered. Our case demonstrates that various neurological symptoms, such as abnormal behavior, rarely occur due to recurrent hypoglycemia in patient with insulinoma.