Multiple endocrine neoplasia type 1 is an autosomal dominant disease caused by the MEN1 germline mutation. A 25-year-old male was admitted for loss of consciousness. Initial laboratory data showed hypoglycemia and hypercalcemia. The image study showed two insulinoma in the pancreas head and body. MIBI scan was positive in the left lower parathyroid gland. After diagnosis of insulinoma and hyperparathyroidism, MEN1 was suspected, but there was no family history of endocrine disease. Enucleation of the insulinoma in the pancreatic head and body was performed. After the operation, the blood sugar level was normalized and no hypoglycemic symptoms were observed. Testing of germline mutations of the MEN1 gene was performed by direct DNA sequence analysis after obtaining informed consent. In the genetic study, a frameshift mutation was found in exon 2 which deleted 16 nucleic acids (c.326_341del16) and resulted in a truncation at codon 113. This mutation was not reported previously. We found a novel and de novo mutation of the MEN1 gene. Genetic study is necessary in case of young-age, multiple endocrine tumors.