Background Hypocalcemia may develop even in the presence of normal postoperative parathyroid hormone (PTH) concentrations. We aimed to identify risk factors of hypocalcemia in patients with normal PTH concentration early after total thyroidectomy (TT). Methods We included 1,504 consecutive patients who underwent TT between January 2012 and December 2013. Significant hypocalcemia was defined as serum calcium concentrations of Results Overall, 333 patients had subnormal PTH 4 hours after surgery (4-hour PTH; Conclusion Female sex, toxic goiter, and 25OH-VD deficiency are not risk factors for post-TT hypocalcemia. Relative parathyroid insufficiency seems to be the principal mechanism of post-thyroidectomy hypocalcemia, even in patients with normal postoperative PTH concentrations.