In some patients with insulinoma, surgery is not possible due to either difficulties in detecting the tumor or advanced age. These patients need medical treatment for hypoglycemia. We report a case of benign insulinoma using the long-acting octreotide formulation, octreotide long-acting repeatable (octreotide LAR), as a medical therapy. A 67-year-old woman was referred to our hospital for examinations of hypoglycemia. A blood sample taken during a hypoglycemic episode revealed low plasma glucose concentration, hyperinsulinemia and a high C-peptide level. An abdominal CT scan demonstrated a hypervascular tumor in the body of pancreas. She was diagnosed with insulinoma. As the patient refused surgical resection of the pancreas tumor, we started to use the somatostatin analogue, octreotide, for treatment of hypoglycemia. After the treatment her plasma glucose levels were elevated and serum immunoreactive insulin (IRI) levels were decreased. For long-term treatment, we changed the treatment from daily subcutaneous injection of octreotide to monthly intramuscular administration of octreotide LAR. This treatment was also effective and hypoglycemic attacks disappeared. Both plasma glucose levels and serum IRI levels were improved. Our case demonstrated that octreotide LAR was useful for long-term medical treatment of insulinoma.