Ultrasonography (US) represents the most sensitive and efficient method for the evaluation of the thyroid and parathyroid glands. Infectious and autoimmune thyroiditis are common diseases, usually diagnosed and followed up by clinical examination and laboratory analyses. Nevertheless, US plays an important role in confirming diagnoses, predicting outcomes and, in autoimmune hyperthyroidism, in titrating therapy. Conversely, in nodular thyroid disease US is the imaging method of choice for the characterization and surveillance of lesions. It provides consistent clues in predicting the risk of malignancy, thus directing patient referral for fine-needle aspiration (FNA) biopsy. Suspicious US features generally include marked hypoechogenicity, a shape taller than it is wide, ill-defined or irregular borders, microcalcifications and hardness at elastographic evaluation. Finally, the role of US in thyroid cancer is to evaluate extension beyond the thyroid capsule and to assess nodal metastases or tumor recurrence. The main application of US in parathyroid diseases is represented by primary hyperparathyroidism. In this condition, US plays a role after biochemical diagnosis, and it should always be strictly performed for localization purposes. In both thyroidal and parathyroid diseases, US is recommended as a guide in FNA biopsies.