The term goiter refers to any enlargement of the thyroid gland. However, most goiters are caused by a nonneoplastic, dynamic process in which there is hyperplasia and regression of the follicular epithelium and accumulation of colloid within the enlarged follicles. Grossly, this can lead to the development of multiple nodules of varying sizes within the gland, termed multinodular goiter. Often the largest or dominant nodule is the target of the fine needle aspiration (FNA). Iodine deficiency is a major cause of multinodular goiter in some countries; however, in geographic areas where dietary iodine is sufficient, the etiology of multinodular goiter is unknown. It may involve abnormalities in thyroid hormone production and variable sensitivity of follicular cells to thyroid-stimulating hormone (TSH). For unclear reasons, multinodular goiters are more common in women and increase with age.