Hypothyroidism is a common endocrine disease with reduced systemic metabolism, but the initial diagnosis is rare in oral and maxillofacial surgery. Due to the nonspecific symptoms, it is easy to be misdiagnosed and missed diagnosis which results in serious consequences. This paper presents a case of severe hypothyroidism which was characterized by airway obstruction, facial swelling, unexplained anaemia and bipedal edema after orthognathic surgery. With review of relevant literatures, this article discusses the risk factors, symptoms, diagnosis and therapy of hypothyroidism.