Thyroid nodules constitute by far the most common disorder of the endocrine system. Epidemiological studies have indicated that approximately 5% of women and 1% of men resident in iodine-sufficient areas have palpable thyroid nodules. However, by the age of 60 years about 50% of the general population is estimated to have at least one thyroid nodule. Indeed, the reported prevalence of a "thyroid incidentaloma" is up to 70% when neck/carotid artery ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) is performed for other indications. Of those with a nodule, 7-15% will have a thyroid carcinoma. The objective of this article is to present updated information on the definition, prevalence, imaging and functional features of thyroid nodules and to provide guidance on the optimal assessment, treatment and follow-up strategy. The endocrinologist dealing with a patient with a thyroid nodule has to consider two main clinical issues: (i) the possibility of thyroid hormonal excess (hyperthyroidism) and (ii) the risk of malignancy. The former is determined by the assessment of the serum concentrations of thyroid stimulating hormone (TSH), as well as of peripheral thyroid hormones and a thyroid radionuclide scan, if necessary; the latter is achieved by the use of thyroid ultrasonography, as well as fine needle aspiration cytology (FNAC) and serum calcitonin measurement, if necessary. These assessments will guide management, which can vary from simple follow-up to surgical resection. The indications for surgical management, simple follow-up, conservative therapy or treatment with radioactive iodine are discussed.