Recent evidence for the clinical significance of postoperative hyponatremia after urologic surgeries remains scarce. We examined the incidence, risk factors, and outcomes of electrolyte imbalance in urologic surgery. Patients with newly developed hyponatremia, defined as a sodium level lower than 135 mEq/L within 7 days after surgery, were included in our study group. The primary outcome was progression to end-stage renal disease (ESRD). Secondary outcome was composition of progression to ESRD and creatinine doubling/eGFR halving from baseline. A survival analysis with a multivariable Cox proportional hazard model was performed. We included 9,206 cases of bladder, prostate, ureter, and kidney surgery. Incidence of new-onset postoperative hyponatremia was 15.4% (1,414/9,206). Postoperative hyponatremia mostly developed in patients with high-risk perioperative characteristics. The development of postoperative hyponatremia was independently associated with progression to ESRD (adjusted HR 1.343, 95% CI 1.082-1.680, P = 0.007). The secondary outcome was also related to the electrolyte imbalance in prostate (adjusted HR 1.729, 95% CI 1.145-2.612, P = 0.009) and kidney (adjusted HR 1.339, 95% CI 1.099-1.632, P = 0.004) surgery. Postoperative hyponatremia in urologic surgery was a common electrolyte imbalance in patients with high-risk perioperative status, and associated with worse renal prognosis.