The main purpose of thyroid FNA (fine needle aspiration) is to separate malignant and possibly malignant nodules from benign thyroid lesions. Every patient with thyroid nodule is a candidate for FNA. Before a decision to perform an FNA, a complete history, a physical examination directed to the thyroid and cervical lymph nodes, a serum thyrotropin level, and thyroid ultrasound should be obtained. Thyroid lesion with a maximum diameter greater than 1.5 cm or nodule of any size with sonographically suspicious features is an indication for FNA. Ultrasound-guided FNA of the thyroid is recommended. The requisition form that accompanies FNA should contain the identifying data, location and size of the nodule, and relevant laboratory and clinical data. FNA diagnosis of thyroid disease is a clinicocytologic diagnosis, and correlation with clinical findings is mandatory for success. Thyroid FNA classification scheme consists of a four diagnostic categories according to the risk of malignancy: benign lesions, indeterminate lesions according to malignancy, malignant tumors, and non-diagnostic. Ancillary studies (immunocytochemistry, RT-PCR, flow cytometry) are usually helpful in borderline cases.