Various structural problems including adrenal insufficiency, excess insulin production from insulinoma, and islet hyperplasia can also cause hypoglycemia.[8] Although the causes of IAS are unclear, the use of sulfhydryl group-containing medications such as methimazole (MTZ) and the HLA-DRB1∗0406 genotype have been reported to be predisposing factors.[9,10] As relatively few cases have been reported in Taiwan, herein we share our experience of a case of MTZ-induced IAS to raise awareness of this potentially life-threatening disease. This evidence concerns the gene INS and pancreatic insulinoma.