One of the most common constitutional chromosomal abnormalities, 22q11.2 microdeletion (del22q11.2) syndrome has diverse medical complications, such as congenital heart defect, hypocalcaemia, and immune deficiency, which require coordinated multidisciplinary care. Until now, the natural history of hypocalcaemia in chromosome del22q11.2 syndrome had been only partly documented, but there has been limited recognition of the importance of calcium status during the postoperative period when altered calcium status may be associated with serious complications. The goals of our study were (1) to delineate the clinical characteristics of serum calcium in patients with del22q11.2 during the postoperative period and (2) to make recommendations for the investigation and management of del22q11.2 patients after cardiac correction. This study included 22 children diagnosed with del22q11.2 syndrome and 110 children without del22q11.2 syndrome from Nanjing Children's Hospital. Clinical examinations and blood ionized calcium testing were reviewed retrospectively. A comparative study of postoperative calcium levels and complications of del22q11.2 patients with nondeletion patients was performed. Association between postoperative hypocalcaemia and adverse incidents after cardiac correction was also examined. Postoperative hypocalcaemia was observed among 86.4% of del22q11.2 patients and among only 47.3% of nondeletion subjects. The difference was statistically significant (P = 0.0017). Patients with del22q11.2 syndrome also had a much sharper decrease in serum calcium levels during the first 6 h after surgery than nondeletion patients. Postoperative clinical analysis showed that del22q11.2 patients with hypocalcaemia experience more postoperative complications (18 of 19) and greater mortality (5 of 19) after cardiac correction than del22q11.2 patients without normal calcium levels and nondeletion patients. Del22q11.2 children have high susceptibility of hypocalcaemia during the postoperative period, and this low calcium status after cardiac correction may be associated with significant risk of postoperative complications and mortality in patients with del22q11.2.