BACKGROUND Calcium and calcitriol supplements are standard for patients with post-thyroidectomy serum calcium <2.0 mmol/L; however, we wondered whether we overtreat post-thyroidectomy hypocalcemia with intraoperative parathyroid hormone (PTH). We examined quick-intraoperative intact PTH (QiPTH) assay results to find a suitable treatment for post-thyroidectomy hypocalcemia. METHODS We studied 197 bilateral thyroidectomy patients. Post-thyroidectomy hypocalcemia was defined as serum calcium <2.0 mmol/L. A QiPTH assay was done 15 min after the thyroidectomy (QiPTH(15)), and hypoparathyroidism was defined as PTH <15 ng/L. The QiPTH(15) assay was used to determine the effects of the thyroidectomy on postoperative PTH levels and serum calcium levels. The natural course and medical response of hypocalcemia was observed in patients with a QiPTH(15) ≥ 15 ng/L. RESULTS None of the 187 patients with a QiPTH(15) ≥ 15 ng/L developed postoperative hypoparathyroidism. However, 79 patients developed transient hypocalcemia, and those with Graves' disease (47/94) had significantly (p < 0.05) higher hypocalcemia than those with non-Graves' thyroid disease (32/93). The serum calcium of these 79 patients declined to its lowest level within the first postoperative 18 h. Seven patients with serum calcium <1.75 mmol/L were successfully treated using a calcium supplement only, and the others recovered spontaneously without treatment. CONCLUSIONS When post-thyroidectomy QiPTH(15) was ≥ 15 ng/L, postoperative hypoparathyroidism was excluded, but more than one-third of the patients developed post-thyroidectomy hypocalcemia. However, most of them recovered without treatment, and a few recovered after taking only a calcium supplement. We believe that using QiPTH(15) results as a guide will prevent overtreatment of post-thyroidectomy hypocalcemia.