AbstractBackground: Post-operative hypocalcemia is the common-est complication after thyroidectomy. Post-operative hypoc-alcemia is a major morbidity in patients that undergonethyroidectomy.Aim of Study: We aimed in this study to study patientswith increased risk to develop post thyroidectomy hypocal-caemia and to study early prediction, diagnosis and treatment.Patients and Methods: Type of study was prospectivestudy, study setting was conducted in Ain Shams UniversityHospitals and Kafr El-Sheikh General Hospital, study periodwas 18 month from January 2019 to June 2020. Obtainingapproval from The Institutional Research Board and writteninformed consents from the participants.Results: Most of the current study participants werefemales (78%) with mean age of (41.1±12.11) years. Twentypercent of patients had DM (20%), (14%) were hypertensive, (8%) had IHD and (10%) had other medical condition. Swellingwas the most common clinical presentation (80%). Muti-nodular goiter was the most common US finding (76%),followed be solitary solid mass (20%) and L. Ns enlargement (10%) among our study patients. Follicular lesion was themost common FNA finding (60%), followed by colloid goiter (20%) and Hashimoto's thyroiditis (8%) among our studypatients. Average Ca before was 9mg/dL, and declined to be 8.4mg/dL 24h post-operative and 8.5mg/dL 48h post-operativewith statistically significant differences (p < 0.001). Hypocal-cemia was founded in 10 (20%) of our patients after totalthyroidectomy it was manifested in 6 (12%) patients andasymptomatic in 4 (8%) patients.Conclusion: Serum calcium concentrations have been thebasis of identification of post-operative hypocalcemia howeverthis has been replaced by PTH levels being more sensitiveand specific to the early prediction of transient as well aspermanent hypocalcemia.