<p>Insulinoma is the most common functioning pancreatic cell tumor, and is characterized by the Whipple triad and usually benign, neuroendocrine tumor of the pancreas. Gastrinoma is characterized by hypergastrinemia, ulcer disease, and/or diarrhea, and is possibly caused by both intra- and extra-pancreatic neuroendocrine tumors that are frequently malignant. In this report, we show a rare case of insulinoma complicated with hypergastrinemia in the subject under treatment of type 2 diabetes mellitus. Selective arterial calcium stimulation test (SACST) is suitable for localizing both insulin and gastrin-secreting tumors. Interestingly, in this case, the arterial stimulation lesion was different from the venous sampling lesion in the SACST for insulin and gastrin-secreting localization. We should know that insulinoma is sometimes complicated by the over-secretion of another functioning hormone such as gastrin. Moreover, we should know that after proper excision of the tumor and pancreas lesion, over-secretion of hormones such as insulin and gastrin is reduced and symptoms are improved.</p>