Generally, it is considered that visceral fat brings insulin resistance and hyper-insulinemia, in the mechanisms of metabolic syndromes. However, whether hyperinsulinemia brings about accumulation of visceral fat is not clear. We followed a case of insulinoma that caused primary hyperinsulinemia, and measured the change in visceral fat and insulin resistance before and after surgical resection of the insulinoma. A 58-year-old woman was admitted to investigate the cause of spontaneous hypoglycemia. An oral glucose tolerance test (OGTT) showed hyperinsulinemia with a high basal level and a glucagon infusion test showed an abnormally high insulin level. Abdominal computed tomography (CT) scan showed an accumulation of visceral fat. Selective celiac angiography showed a pancreatic tumor shadow. Under a diagnosis of insulinoma, the pancreatic body and tail were removed. At 3 months after the operation, the visceral fat area had decreased from 132.6 to 64.2 cm(2). The fasting serum total cholesterol and triglyceride were also reduced. In addition, high-density lipoprotein cholesterol and preheparin serum lipoprotein lipase mass had increased. The midband on the polyacrylamide gel disc electrophoresis of lipoproteins, which appeared before operation, had disappeared completely. An OGTT showed a non-diabetic pattern after the operation. These results suggest that hyperinsulinemia might be one of the factors that enhance visceral adiposity and insulin resistance.