Fine-needle aspiration cytology (FNAC) is a more mature diagnostic technique. FNAC has been clinically proven to be less invasive, easier to perform, has a higher diagnostic rate, and is less expensive than other conventional methods of thyroid nodule examination. FNAC is generally not limited by the size of the thyroid nodule and can be performed as long as the patient is clinically well. There are almost no complications and no reports of tumor implantation, and the procedure can be repeated. It is well documented that FNAC of thyroid nodules is very reliable for the diagnosis of benign nodules, with a false-negative rate of about 1.3-11.5%, with an average of 5.2%. False negatives occur more often in cystic nodules, and papillary carcinoma is the main type of cystic carcinoma. In order to minimize the false negative rate, it is crucial to aspirate enough representative tissue. The initial negative smear is often not indicative of the problem and should be repeated in the cystic wall or margin of the lesion to obtain as much representative tumor tissue as possible; another reason for false negatives is that the tumor is small and deep or obscured by other benign nodules, so the real cancer tissue cannot be obtained. The rate of cytologic diagnostic false positives is very low, and the most frequent false positives of FNAC are atypical adenomas and hyperplastic nodules with papillary structures. The limitations of FNAC, besides being influenced by the level of the pathological diagnostician and the site of sampling, are that it can only observe cellular morphology and structural changes and lacks an understanding of the overall tissue structure. Sometimes the differential diagnosis of FNAC is very difficult, for example, FNAC can confirm follicular thyroid tumors, but cannot distinguish follicular adenoma or follicular-like adenocarcinoma, because the latter must have invasion of the envelope to make the diagnosis, and FNAC cannot understand these conditions of the tumor. Indications for thyroid fine needle aspiration 1. previous history of thyroid cancer 2. family history of thyroid cancer 3. patients with hard, irregular, poorly mobile nodules palpated during thyroid examination 4. patients with pressure symptoms or hoarseness 5. differential diagnosis of benign thyroid nodules 6. nodules over 1-1.5 cm palpable or detected by imaging 7. differentiation of Hashimoto’s hyperthyroidism or Graves’ disease 8. ultrasound examination Confirmation of a nodular lesion