Background: Hypocalcaemia is a well-recognized complication of thyroid surgery. It is most often transient event that occurs after extensive thyroid resection Aim of the study: To determining the incidence of hypocalcaemia after thyroid surgery and find out the risk factors involved as the patient age, gender and clinical diagnosis. Patients and methods: This prospective study is carried out on 106 patients who underwent thyroid surgery for various thyroid diseases, by different surgeon at Al-Hilla teachinghospital form January 2013 to January 2014. Patient age, gender and serial serum calcium measurements were done as well as details of the operation; as ligation of the inferior thyroid artery, histopathological results. Hypocalcaemia was considered transient if it was resolved within 6 months and permanent if it persisted after 6 months. Results: This study show that the incidence of post-thyroidectomy hypocalcaemia is 30%. The majority of the cases (24%) was transient, while the permanent was only (6%) of cases,whom had total thyroidectomy and uni or bilateral ligation of the inferior thyroid artery. Conclusions: Post thyroidectomy hypocalcaemia is a relatively common complication, but it is transient in the majority of the patients. Its incidenceis related to the extent of the surgery