Whether a thyroid nodule 5mm*3mm is serious or not needs to be determined according to its nature. If it is a benign asymptomatic nodule, it is usually not serious, but may be more serious if there are pressure symptoms or suspicion of malignancy. 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. Evaluation of the morphologic features of the nodule, sometimes in combination with its blood supply, can help ultrasound determine the risk of malignancy in thyroid nodules. Benign asymptomatic thyroid nodules are usually treated with regular ultrasound examinations of the thyroid gland. If there are symptoms of pressure such as dyspnea or dysphagia, or if there is a tendency for malignant changes, aggressive surgical treatment is required. If you find a thyroid nodule of 5mm*3mm, you should consult a professional physician for diagnosis and treatment to avoid delaying your condition.