Background <p>This study aimed to determine the incidence of permanent hypoparathyroidism (PH) after thyroidectomy and evaluate the association between PH and perioperative surgical, clinical, and biochemical factors.</p> Methods <p>Patients who underwent total or completion thyroidectomy between 2017 and 2024 were retrospectively evaluated. PH was defined as a serum parathyroid hormone (PTH) level &lt; 15 pg/mL and the need for active vitamin D, with or without calcium supplementation, to prevent hypocalcemic symptoms persisting for at least 6 months postoperatively. Patients were categorized according to PH status, and clinical, surgical, and biochemical parameters were analyzed.</p> Results <p>Among the 498 eligible patients, 18 (3.6%) developed PH. A postoperative day 1 PTH level ≤ 7 pg/mL predicted PH with 86.7% sensitivity and 90.3% specificity and was an independent risk factor in multivariate analysis (odds ratio [OR]: 16.60, <i>p</i> &lt; 0.001). Completion thyroidectomy was also independently associated with PH (OR: 6.14, <i>p</i> = 0.027). Postoperative day 1 calcium ≤ 8.3&#xa0;mg/dL (OR: 14.20, <i>p</i> &lt; 0.001) and the presence of parathyroid tissue in the surgical specimen (OR: 6.25, <i>p</i> &lt; 0.001) were significant in univariate analysis but not in multivariate analysis (<i>p</i> = 0.08 and <i>p</i> = 0.056, respectively).</p> Conclusions <p>Permanent hypoparathyroidism remains a clinically significant complication of thyroidectomy, with an incidence of 3.6% in our cohort. A postoperative day 1 PTH ≤ 7 pg/mL was independently associated with PH and demonstrated an excellent negative predictive value (99.4%), supporting its clinical utility for ruling out PH rather than confidently predicting it. Completion thyroidectomy was also independently associated with PH. Given the limited number of events, these findings warrant validation in larger, prospective cohorts.</p> Clinical trial number <p>Not applicable.</p>