AIM: The aim of this study is to determine an early measured serous PTH cut-off value below which it ‘s possible to predict post-thyroidectomy hypocalcaemia outbrake. MATERIALS OF STUDY: Ninety-three consecutive patients having a benign thyroid pathology were submitted to total thyroidectomy. In all the patients serous post-surgery intact PTH and total calcium were measured within an hour from weaning. 65 patients were measured a second time 18 hours from surgery. We searched for a correlation between the post-surgery PTH values at 1 and 18 hours from surgery with the calcemia at 1 and 18 hours from surgery. We carried out a one-year follow-up for each patient. Hypocalcemia developed in 26 patients (27.95%). It was transitory in twenty-two patients (23.65%) and permanent in 4 patients (4.3%). No correlation was found between PTH1 and Ca1 (p=0.8). Statistically relevant correlation (p=0.008) was found between PTH1 and Ca2. The correlation between PTH2 and Ca2 (p=0.001) turns out to be even more relevant. We also calculated a found that 9.5 pg/dl was PTH1 cut-off value below which it is possible to predict hypocalcemia onset (p=0.001). DISCUSSION AND CONCLUSIONS: Early post-surgery PTH measuring is a highly predictive test of post-surgery hypocalcemia. We identified a PTH1 cut-off value of 9.5 pg/dl, below which hypocalcemia onset is extremely frequent. This assessment permits us to estabilish an adequate drug prophylaxis, thus avoiding the related symptoms. We can also perform one-day surgery thyroidectomy in patients showing normal PTH values.