Loeys-Dietz syndrome is a hereditary connective-tissue disorder first reported in 2005. It is caused by genetic defects in the transforming growth factor-beta (TGF-β) signaling pathway. TGF-β signaling plays an important role in connective-tissue development, differentiation, and homeostasis. Dysregulation of TGF-β signaling causes various defects in the skull, face, skeletal system, skin, and blood vessels. Symptoms of Loeys-Dietz syndrome include scoliosis, spider finger, joint laxity, club foot, hypertelorism, and cleft palate. In addition, aortic aneurysm, aortic dissection, bleeding tendency, delayed wound healing, allergic disease, and autoimmune disease have been reported. Here, we describe an 11-year-old male with type 1 diabetes mellitus who had frequent epistaxis and easy bruising from an early age, along with skin and joint hyperextension, atrophic scars, and long limbs. He was suspected of having a hereditary connective-tissue disorder and was diagnosed with Loeys-Dietz syndrome type 1 by next-generation sequencing. Similar to Marfan syndrome and Ehlers-Danlos syndrome, this disease has a high risk of aortic aneurysm and aortic dissection. In addition, because aortic dissection can occur at a young age, early diagnosis and periodic examination and treatment for cardiovascular diseases are necessary.