Hypoparathyroidism is a rare endocrine disease with insufficient parathyroid hormone levels. Replacing the missing hormone is not yet a standard therapy. The objective of this retrospective cohort study was to evaluate if the usual therapy regimens of postsurgical hypoparathyroidism with calcitriol have a negative effect on renal function. We performed a chart analysis of patients who were seen in a tertiary care hospital in Brussels, Belgium. A total of 101 subjects were identified as patients with permanent post-surgical hypoparathyroidism, based on the hospital records of patients who underwent a total thyroidectomy between 1996 and 2016, while still being treated with calcitriol. Patients with pre-existing renal insufficiency and/or active malignancy were excluded. The cohort was predominantly female of Caucasian origin. Renal function was evaluated before and after surgery (with a maximum follow-up of 12 years), using the CKD-EPI equation. A multivariate linear regression model was used to correlate renal function decline with the duration of calcitriol therapy, while correcting for the mean calcium phosphate product and age. We found a statistically significant (p=0.027) relationship between the duration of calcitriol treatment and renal function decline at a rate of 1.06 ml/min/1.73 m2 per year of calcitriol therapy. Our study, although being retrospective, is the first one to demonstrate a relationship between the cumulative use of calcitriol therapy and renal function decline.