Hyperthyroidism is short for hyperthyroidism, a thyrotoxic condition caused by the thyroid gland itself producing too much thyroid hormone. It is not possible to generalize about the severity of hyperthyroidism. The severity of hyperthyroidism symptoms and signs is related to factors such as the length of the medical history, the degree of hormone elevation, and the age of the patient. The main symptoms of hyperthyroidism are: excessive eating, weight loss, fear of heat, excessive sweating, palpitations, agitation, irritability, insomnia, fatigue, increased frequency of stools or diarrhea, protruding eyes, enlarged thyroid, and scanty menstruation in women. It may not cause serious consequences when appropriate treatment is carried out. However, there are some cases that may lead to serious consequences, such as hyperthyroidism with protruding eyeballs, severe eyeball fixation, incomplete eyelid closure, corneal ulcers formed by corneal exposure, total ophthalmitis, and even blindness; severe hyperthyroidism untreated or inadequately treated may lead to thyroid crisis, which may be characterized by heart failure, shock, and coma in severe cases. The death rate of hyperthyroidism crisis is more than 20%; indifference type hyperthyroidism, mostly seen in elderly patients, the onset of insidious and inconspicuous symptoms, easy to be ignored or misdiagnosed, thus delaying the condition, resulting in adverse consequences, and so on. Therefore, whether hyperthyroidism is serious or not should be judged according to the patient’s condition and treatment. Early, mild or treated hyperthyroidism may not be serious, but if it is not treated or inadequately treated, it may cause serious consequences.