Background: hypocalcaemia, which is a major contributing factor for delayed hospital discharge, occurs in many patients following total thyroidectomy. Parathyroid hormone (PTH) measurement has been proposed as a marker of this condition. Aim: the aim of this study was to evaluate the reliability of perioperative parathyroid hormone measurement to predict post-total thyroidectomy hypocalcaemia. Patients and methods: a prospective randomized study was conducted in the period between July 2015 and September 2017 in Ain Shams University, General Surgery Department, Endocrine Surgery Unit, Cairo, Egypt. The study was conducted on sixty patients for whom total thyroidectomy was done. Parathyroid hormone was measured pre-operative and 6 hours postoperative, and serum Ca was measured daily to predict hypocalcaemia. Patients were evaluated for symptoms of hypocalcaemia and treated with calcium and vitamin D supplementation as necessary. Results: the study included 60 patients, 12 males and 48 females with mean age 39.1+ 16.52 (20-65). Co morbid conditions included HTN, DM, ISHD and COPD. Most patients had nodular goiter (48 patients) whether unilateral or bilateral. 63.3% of patients had follicular lesion by FNABC. All patients underwent total thyroidectomy. Hypocalcemia developed in 16.7% (10 of 60) of the patients. Best cut off was 66% reduction giving 77% Sensitivity and 91.4% Specificity. Positive predictive value was 85% and negative predictive value was 94%. Conclusion: the evaluation of PTH and corrected calcium levels 6 hours after thyroidectomy allows for an accurate prediction of the trend of hypocalcemia. This study enables us to discharge most patients safely within 24 hours after total thyroidectomy.