Thyroid nodules are a common finding in the general population. They may present with symptoms of pressure in the neck or may be discovered during physical examination. Although the risk of cancer is small, it is the main reason for workup of these lesions. Measurement of thyroid-stimulating hormone can identify conditions that may cause hyperfunctioning of the thyroid. For all other conditions, ultrasonography and fine-needle aspiration are central to the diagnosis. Lesions larger than 1 cm should be biopsied. Lesions with features suggestive of malignancy and those in patients with risk factors for thyroid cancer should be biopsied, regardless of size. Smaller lesions and those with benign histology can be followed and reevaluated if they grow. The evaluation of thyroid nodules in euthyroid and hypothyroid pregnant women is the same as in other adults. Thyroid nodules are uncommon in children, but the malignancy rate is much higher than in adults. Fine-needle aspiration is less accurate in children, so more aggressive surgical excision may be preferable.