Noonan syndrome (NS) is a genetic disorder characterized by craniofacial dysmorphism, chest deformities, congenital heart defects, and bleeding disorders. Although patients with NS have a high prevalence of orofacial deformity, few reports are available on their anesthetic management during orthognathic surgery. This case report describes a 31-year-old female with NS, anemia, hypertrophic cardiomyopathy, and mild mitral valve regurgitation who experienced severe bleeding during orthognathic surgery. After treating her anemia with oral iron therapy and subcutaneous epoetin β, 4 units of autologous blood was deposited prior to surgery. General anesthesia was induced with remifentanil and propofol and maintained with sevoflurane, remifentanil, and fentanyl. Despite mild hypotensive anesthesia (targeted mean arterial pressure of 65 mm Hg) with nitroglycerine and intravenous tranexamic acid for bleeding, adequate hemostasis was difficult to achieve and led to severe blood loss (1442 mL). Therefore, the 4 units of autologous blood and 2 units of packed red blood cells were transfused. Her postoperative course proceeded uneventfully without abnormal postoperative bleeding. Because patients with NS can have difficulty with hemostasis, vascular malformations, and fragile blood vessels, extensive hematologic evaluation and thorough preparation for unexpected bleeding are crucial to accomplish orthognathic surgery.