The thyroid is a gland responsible for production of thyroid hormones. Thyroid hormones are essential to regulate metabolism and other key body functions. Signs and symptoms of thyroid disease may occur if thyroid hormone levels are not in the normal range. In addition to altered function, thyroid structural abnormalities may occur, ranging from benign (non cancerous) to malignant (cancer). Depending on the underlying problem, blood tests, imaging, and biopsy may be used to make a diagnosis. Treatment depends on the particular thyroid disease that is present.