['Decreased renal function has been consistently included among factors prompting recommendation for surgery in primary hyperparathyroidism (PHPT). However, most retrospective studies addressing this issue did not show an improvement in renal function after parathyroidectomy (PTX). The aim of this study was to investigate changes in renal function after PTX in PHPT patients subdivided according to renal function at diagnosis.', 'This was a retrospective cross-sectional study.', 'We studied 109 consecutive PHPT patients before and after PTX. Biochemical evaluation included fasting total and ionized serum calcium, phosphate, creatinine, immunoreactive intact PTH, and 25-hydroxyvitamin D3 levels. Glomerular filtration rate (GFR) was assessed with the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.', 'Mean (± SD) CKD-EPI estimated GFR (eGFR) at diagnosis was 82.4 ± 19.3 mL/min/1.73 m(2) (median, 84.8 mL/min/1.73 m(2); interquartile range, 68.5-94.2 mL/min/1.73 m(2)). Patients with eGFR equal to or higher than 60 mL/min/1.73 m(2) (group 1, n = 95) were significantly younger than patients with eGFR lower than 60 mL/min/1.73 m(2) (group 2, n = 14; P < .0003). After PTX, eGFR did not change in patients of group 2 (P = .509), whereas it was significantly reduced in patients of group 1 (P < .0002). The difference in eGFR between baseline and post-PTX values was correlated negatively with baseline serum creatinine (R = -0.27; P = .0052) and positively with baseline CKD-EPI eGFR (R = 0.32; P = .00062). At multiple regression analysis, only systolic blood pressure and baseline CKD-EPI eGFR were independent predictors of GFR variation.'] Does parathyroidectomy halter the Deterioration of Renal Function in Primary Hyperparathyroidism?