Insulinoma is the most common endocrine tumor of the pancreas. It arises from the beta-islet cells of Langerhans. Insulinomas synthesize and secrete insulin autonomously in the presence of low blood glucose levels, causing spontaneous hypoglycemia and characteristic clinical symptoms. The authors examined data the from the most important international research projects on this topic during the past 20 years. Insulinomas are rare, with an annual incidence of 0.5 per million population. Up to 90% patients have benign solitary pancreatic insulinomas. People of all ages can be affected with this neoplasm. The authors reported a case of a large insulinoma of the body and tail of the pancreas, with atypical psychic symptoms. A distal pancreatectomy with splenectomy was performed. No surgical complications occurred in the postoperative course. The psychic symptoms were emphasized with refusal of food. The patient underwent Parenteral Nutrition and was discharged 24 days after the operation. The surgical removal of the tumor permitted the patient to recover completely, with glucose and insulin blood levels in normal range.