Background and Objectives：Incidence of hypocalcemia after thyroidectomy varies from 5.4 to 83%, and permanent hypocalcemia from 0.5 to 8%. The purpose of this study was to determine incidence and risk factors for the development of hypocalcemia and permanent hypocalcemia after thyroidectomy. Materials and Method：The medical records were reviewed for 130 patients who underwent thyroid surgery at the Department of Otolaryngology, Dongsan Medical Center, Keimyung University from January 1998 to June 2002. The subjects were reviewed according to sex, various thyroid diseases, unintentional removal of parathyroid gland, autotransplantation of parathyroid gland and various surgical modality that would affect postoperative hypocalcemia. Hypocalcemia was defined as a serum calcium level under 8.0 mg/dl on at least two consecutive measurements regardless of symptoms. Permanent hypocalcemia was defined for cases in which hypocalcemia persisted more than 6 months after thyroidectomy. Results：Among 130 patients, 43 patients (33.1%) had hypo-calcemia and 9 patients (6.9%) permanent hypocalcemia. Factors significantly predictive of postoperative hypocalcemia in univariate analysis included malignancy (p<0.001), extensive operation (total thyroidectomy, total thyroidectomy with neck dissection)(p<0.001) and unintentional removal of parathyroid gland (p<0.001). Independant risk factors on multivariate anal-ysis were malignancy (p=0.027) and unintentional removal of parathyroid gland (p=0.048). Conclusion：Our study showed that the incidence of hypocalcemia after thyroidectomy was 33.1% and permanent hypocalcemia 6.9%. Our study found malignancy, extensive surgery, unintentional removal of parathyroid gland to be statistically significant risk factors. Hypo-calcemia can be kept to a minimum by profound knowledge of anatomy of thyroid and parathyroid gland, meticulous surgical technique and delicate autotransplantation of parathyroid gland.