OBJECTIVE To evaluate the incidence and predictors of post-thyroidectomy definitive hypocalcemia and hypoparathyroidism. METHODS We assessed ionic calcium preoperatively and postoperatively (first, second and 30th day) in 333 patients undergoing thyroidectomy. In those presenting hypocalcemia, measurements were also made 90 and 180 days after surgery, when parathormone was also dosed. Patients were grouped according to the presence or absence of hypocalcemia and evaluated according to age, gender, thyroid function, thyroid volume, number of parathyroid glands identified and need to parathyroid reimplantation, type of operation, operative time, and histopathological diagnosis. RESULTS The incidence of temporary hypocalcemia was 40.8% (136 patients), and of definitive hypoparathyroidism 4.2% (14 patients). Reoperation or total thyroidectomy, neck dissection, hyperthyroidism, operative time and age above 50 years were factors related to higher incidence of hypocalcemia and definitive hypoparathyroidism (p <0.05). CONCLUSIONS predictors of postoperative hypocalcemia included age (> 50 years), total thyroidectomy, reoperation, neck dissection and operative time. The predictors of post-thyroidectomy definitive hypoparathyroidism included type of operation, histological diagnosis and hyperthyroidism.