Thyroid nodule 0.4cm can not judge whether it is serious or not, but also according to whether it has clinical manifestations, whether malignant transformation to judge. Asymptomatic benign thyroid nodules are generally not serious. If a simple thyroid nodule is not accompanied by clinical manifestations, thyroid function is normal, and thyroid ultrasound suggests that a benign thyroid nodule is likely, such nodules are generally not serious and only require regular observation. However, if the size of the thyroid nodule increases significantly and pressure symptoms such as dyspnea and dysphagia occur, or if ultrasound or puncture biopsy suggests that the thyroid nodule has a malignant tendency, such cases may be more serious and may require surgical treatment. Patients with thyroid nodules 0.4cm should be diagnosed and treated under the guidance of a specialized doctor.