Thyroid surgery is generally recommended for malignant conditions and for some benign thyroid disorders. Many patients report weight gain after thyroidectomy especially during the first months following surgery. Studies on patients with Graves’ disease treated either with antithyroid drugs or radioiodine confirm that these patients frequently gain weight after restoration of thyroid function. Other studies have also shown that there is considerable weight gain after thyroidectomy for both nodular goiter and thyroid cancer. Transient hypothyroidism during the postoperative period is often thought to be associated with weight gain after thyroidectomy. The role of a number of adipocytokines and their interaction with the thyroid function has been investigated in the pathogenesis of weight changes. Levothyroxine replacement or suppressive therapy after thyroidectomy has a different impact on the metabolic parameters independent of TSH levels. The long-term effects of the impaired T3/T4 ratio are not fully understood as there are no sensitive markers to assess the biological response of target organs and tissues. Future studies are needed to identify such parameters, provide new considerations for the treatment of patients after total thyroidectomy, and help determine individual target hormone levels to ensure a sustained euthyroid state.