Aim: Parathyroidectomy causes significant changes in mineral metabolism in patients with primary hyperparathyroidism (PHPT). Hypomagnesemia may be seen after parathyroidectomy with unknown mechanisms. Our study aimed to evaluate the severity of hypomagnesemia and its correlation with clinical and biochemical variables after the surgery. Materials and Methods: A retrospective study was conducted in the patients with parathyroidectomy for PHPT between January 2017 and December 2020 in a single tertiary hospital. All consecutive patients with preoperative and postoperative magnesium levels (n=80) were included. Patients were divided into two groups according to the postoperative first-day serum magnesium levels: patients whose serum magnesium was <1.9 mg/dL (group HypoMg) and patients whose serum magnesium was ≥1.9 mg/dL (group NorMg). Demographic and clinical parameters and biochemical findings were recorded. The incidence of postoperative hypomagnesemia was the primary outcome. Results: The mean age was 56.7±12.2 years. The female to male ratio was 3.21. There were 31 (38.8%) and 49 patients (61.2%) in group HypoMg and group NorMg, respectively. The groups were similar considering demographic and clinical parameters (p>0.05). There were no significant differences in the preoperative serum calcium, adjusted calcium, and parathyroid hormone levels between the groups (p>0.05). Preoperative magnesium levels were significantly lower in the HypoMg group (p<0.001). Postoperative serum magnesium levels were positively correlated with preoperative serum magnesium levels (r=0.719, p<0.001). Conclusion: Postoperative hypomagnesemia may be seen after parathyroidectomy. It was significantly correlated with preoperative hypomagnesemia.