BackgroundHyperthyroidism after parathyroidectomy is not a well-understood complication. We sought to determine the incidence and risk factors of hyperthyroidism after parathyroidectomy. Materials and methodsThis is a prospective study of 91 patients undergoing parathyroidectomy. Pre- and post-operative thyroid-stimulating hormone(TSH) and free thyroxine(T4) levels at two-week follow-ups were collected. Bivariate analyses were conducted to compare demographics, laboratory results, and intraoperative findings between patients with normal and suppressed post-parathyroidectomy TSH. ResultsTwenty-two(24.2 %) patients had suppressed TSH after parathyroidectomy and 2(2.2 %) reported symptoms of hyperthyroidism. All hyperthyroidism resolved within 6 weeks. No patients required medical treatment. Compared to the normal TSH group, the suppressed TSH group had significantly more bilateral explorations(91.0 % vs. 58.0 %, p = 0.006), and superior parathyroid resections(95.5 % vs. 65.2 %, p = 0.006). ConclusionTransient hyperthyroidism is common following parathyroidectomy, which is likely associated with intraoperative thyroid manipulation. Gentle retraction of thyroid glands in parathyroidectomy is warranted, especially during superior parathyroid gland resection.