Whether a thyroid nodule is dangerous or not is related to the size and nature of the thyroid nodule. A malignant thyroid nodule may be more dangerous; in addition, a nodule that is large in size and produces symptoms of pressure such as dyspnea and dysphagia may also be more dangerous; benign and asymptomatic thyroid nodules are generally not dangerous and regular follow-up is sufficient. Ultrasound is the most important imaging tool for evaluating thyroid nodules. Ultrasound can determine whether the nodule is solitary or multiple, the size of the nodule, the morphologic features of the nodule, and the blood supply of the nodule. By evaluating the morphological features of the nodule, sometimes in conjunction with its blood supply characteristics, ultrasound can help determine the risk of malignancy in thyroid nodules. Patients with thyroid nodules should visit a hospital and be treated under a doctor’s supervision.