Purpose <p>We aimed to assess the decline in renal function in patients with chronic postoperative hypoparathyroidism.</p> Methods <p>We performed a multicenter, retrospective cohort study including patients with chronic hypoparathyroidism lasting ≥ 3 years. We evaluated the changes in serum creatinine and estimated glomerular filtration rate (eGFR) before surgery and at the last visit. Changes were evaluated in absolute value (ΔeGFR = eGFR at last visit – eGFR before thyroidectomy) and corrected for time (ΔeGFR/yr = ΔeGFR / time in years).</p> Results <p>We included 236 patients with hypoparathyroidism (85.6% women, median age 47 [37–58] years, median time of follow-up 7.3 [5.0–11.0] years), and 458 control subjects with similar age, gender, and time of follow-up. Before thyroidectomy we found no significant differences in serum creatinine levels or eGFR between patients and controls. At the end of follow-up, ΔeGFR and ΔeGFR/yr in the patients with hypoparathyroidism were −4.87 (−17.0–0.00) ml/min/1.73 m² and −0.68 (–2.31–0.00) ml/min/1.73 m² per year, respectively, whereas in the control subjects these changes were 0.00 (−10.10–4.00) ml/min/1.73 m² (P &lt; 0.001), and 0.00 (−1.34–0.54) ml/min/1.73 m² per year (P &lt; 0.001). In multivariable regression analysis the annual eGFR decline in patients with hypoparathyroidism was related to age (P &lt; 0.001), eGFR before thyroidectomy (P &lt; 0.001), and incident nephrolithiasis (P = 0.028).</p> Conclusion <p>The decline in renal function over time is significantly higher in patients with chronic hypoparathyroidism after thyroidectomy compared to thyroidectomized patients without hypoparathyroidism. Age, preoperative eGFR and nephrolithiasis are the main determinants of renal function loss in these patients.</p>