Introduction
	Nodular thyroid disease is found in approximately 5% of the population at palpation screening and is almost ten-fold more frequent at echographic screening1. Ahigher prevalence is observed in endemic goiter areas. Thyroid nodules are rare in children and adolescents and increase almost linearly with age; females are affected 2-4-fold more frequently than males2. Nodular thyroid disease is a heterogeneous disorder with regard to clinical, functional or histological aspects: nodules may be single or multiple, hyper- or hypo-functioning, benign or malignant. Malignant nodules account for approximately 5% of all nodules. The large majority of them arises from the follicular epithelium and includes well-differentiated carcinomas in approximately 75 % of cases and poorly differentiated or anaplastic in 15 % of cases. Medullary cancer arising from calcitonin producing parafollicular cells account for approximately 10% cases. Thyroid cancer can be a mortal disease: mortality ranges from 10 % of well differentiated tumors, to 50 % of poorly differentiated and medullary and to 100% of anaplastic tumors, respectively. An early diagnosis and treatment is, therefore, of utmost importance to reduce thyroid cancer mortality. However, as malignant nodules are a small minority, the choice to address all nodules to surgical treatment is impractical, cost ineffective and would expose people with benign nodules to unnecessary morbidity and mortality. Fine-needle aspiration biopsy (FNAB) of the thyroid, first described in 19483 and pioneered by Scandinavian Authors in the early seventies4, has now gained wide acceptance as the most accurate diagnostic procedure for distinguishing benign from malignant thyroid nodules5-7. The routine use of FNAB has changed the management of thyroid nodules by allowing to spare unnecessary operations for benign lesions and reducing costs of care. Although apparently simple, thyroid FNAB requires multidisciplinary expertise to give best results. Moreover, it gives limited information in approximately 25 % of cases because of insufficient cellular yield or “indeterminate” diagnoses. This review will focus on the clinical use and limitations of FNAB in the management of thyroid nodular disease.