Causes, Diagnosis and Treatment of Thyroid DiseaseAbout This Hardback The thyroid gland is an endocrine gland located in the neck. It produces hormones that are vital for many different systems throughout the body. When the thyroid releases either too much or too little of these hormones, it results in thyroid disease. The two most common types of thyroid disease are hyperthyroidism and hypothyroidism. Hypothyroidism can be caused by thyroiditis, Hashimoto's thyroiditis, postpartum thyroiditis,