Thyroid diseases are more prevalent in females. This notion is mostly derived from studies conducted in adult subjects, but the knowledge of the relationship between sex and thyroid disease is becoming important for the epidemiological study of aging population. Aging has been proposed to represent a trigger for the development of autoimmune phenomena resulting in the production of both organ- and non-organ-specific antibodies. Studies on the relationship between sex and thyroid autoimmunity in elderly subjects have shown that the age-related prevalence of antithyroid autoantibodies is greater in women >60 yr of age. An increased prevalence of hypothyroidism has been demonstrated in the elderly population. Several factors may affect prevalence, but virtually all studies report higher prevalence rates for either overt or subclinical hypothyroidism in women with advancing age. This gender-related difference, however, has not been demonstrated for hospitalized patients. Difficulties are encountered in the attempt to estimate a sex-related difference in the prevalence of hyperthyroidism in elderly subjects. In most cases, Graves' disease and toxic multinodular goiter represent the cause of the disease with relative proportions depending on iodine intake. However, data on the prevalence of this disorder and on its sex-related frequency are significantly affected by underlying nodularity and functional autonomy. This phenomenon may be even more pronounced when excess iodine intake occurs and when patients are treated with iodine-containing drugs and thyroid hormone therapy. Subclinical hyperthyroidism is more common in women than in men, especially in subjects >70 yr. Both overt and subclinical hyperthyroidism arise from underlying thyroid nodular disease. The low-T3 syndrome is common in the elderly. Due to the fact that the low-T3 syndrome is often derived from underlying diseases, it is difficult do define a sex-related difference in its prevalence. However, in unselected elderly home-dwellers, an independent association of low-T3 syndrome with male gender has been shown. Aging represents an important factor to define the aggressiveness of thyroid carcinomas. Both follicular and anaplastic histotypes of thyroid cancer are more frequently found in elderly subjects. In aging subjects, male sex seems to be highly correlated with the risk of thyroid cancer. In conclusion, epidemiological data from the aging population confirms that men are less affected by thyroid disease than women. However, male sex may represent a risk factor for thyroid cancer in elderly population and this observation should be carefully considered in the evaluation of thyroid nodules in the elderly.