Nodular goiter is the natural evolution of nontoxic goiter, that may be endemic, sporadic or familiar. Iodine deficiency is the cause of endemic goiter, while genetical defects, impairing the thyroid hormone biosynthetic efficiency or altering the number and/or activity of growth factor receptors, play the major role in the pathogenesis of sporadic and familiar nontoxic goiter. The prevalence of nodular goiter is directly related to the degree of iodine deficiency that is still present in several areas of the world. In iodine deficient areas such as some Italian regions, nodular goiter is present in 25-33% of the population, its frequency increasing with age. In iodine sufficient areas the prevalence of nodular goiter is comprised between 0.4 and 7.2% high in iodine deficient areas and about 4% in iodine sufficient countries, its frequency increasing with the age. Dysphagia, dyspnea and coarsening of the voice may occur for esophagous, tracheal or laryngeal nerve compression, respectively. Iodine deficiency has little if any effect on the frequency of thyroid carcinoma, while, with regard to the histological pattern, it leads to an increased ratio papillary/follicular. Thyroid function is normal in uncomplicated nontoxic goiter. However, the evolution of nodular goiter is toward the functional autonomy of nodules that may result in thyrotoxicosis. Hypothyroidism is rare and is usually the result of thyroid autoimmunity. All the cases due to iodine deficiency can be prevented by an adequate iodine prophylaxis that can be accomplished in industrialized countries by the use of sale enriched in iodine.