A 73-year-old woman with malignant insulinoma was treated with 100 μg/day octreotide for unresected insulinoma and liver metastases. The daily administration of the drug induced hyperglycemia after dinner in addition to existing fasting hypoglycemia possibly because this drug suppressed both insulin and glucagon secretion and its blood concentration was unstable. After replacing a daily injection of octreotide with a monthly injection of octreotide long-acting repeatable (LAR), blood glucose levels stabilized within the normal range. The findings of the present study showed that octreotide LAR could be useful for the long-term treatment of unresectable insulinomas.