Thyroid nodule 40mm is considered a relatively large nodule, if it is benign and asymptomatic thyroid nodule, it is generally not serious; if it produces pressure symptoms or malignant thyroid nodule, it is more serious. Thyroid nodule is a lesion caused by localized abnormal proliferation of thyroid cells, and there is a difference between benign and malignant; if it is benign and asymptomatic, thyroid nodule 40mm is not considered serious, and can be rechecked according to the doctor’s instructions; if the thyroid nodule causes pressure symptom or is confirmed to be malignant, it is a more serious situation, and needs to be considered for surgical treatment. Patients diagnosed with thyroid nodules 40mm should go to the hospital and ask the doctor to make a comprehensive judgment based on the specific situation and give a treatment plan.