Background To describe a standardized, efficient, and cost-effective protocol for the diagnosis of temporary/persisting postoperative hypoparathyroidism after (total) thyroidectomy. Methods We included 237 consecutive patients who underwent (total) thyroidectomy without central neck dissection for various indications. Serum calcium (sCa) and intact parathyroid hormone (iPTH) levels were measured prospectively on the morning of postoperative day 1 to predict the long-term parathyroid metabolism. On the morning of postoperative day 2, measurements were repeated. Follow-up was performed at 1 and 6 months postoperatively. Results On the morning of postoperative day 1, patients with iPTH ≥ 15 pg/mL (178/237; 75%) and sCa > 2.0 mmol/L were normocalcemic, and “normal” parathyroid metabolism was predicted. iPTH levels of <10 pg/mL and sCa levels of ≤2.0 mmol/L were present in 33 of the 237 patients (“disturbed” parathyroid metabolism; 14%). A “gray zone” included patients with “uncertain” parathyroid metabolism demonstrating iPTH levels between 10 and 15 pg/mL (26/237; 11%). Patients with “disturbed” and “uncertain” parathyroid metabolism were given oral calcium and vitamin D. On the morning of the second postoperative day, iPTH turned to “normal” in 10 of those 26 (38%) patients, and no further calcium or vitamin D was given. During follow-up, supplemental calcium and vitamin D was able to be stopped in all but 2 patients (“permanent” hypoparathyroidism). Conclusion Measurement of iPTH on the morning after operation allows accurate prediction of postoperative parathyroid function in ≤99% of cases. This simple recommendation is practicable in all surgical units, and is an efficient and cost-effective way to recognize patients who require calcium and vitamin D supplementation.