BACKGROUND: To compare the prevalence of nephrotoxicity between patients with a solitary-functioning kidney versus those with bilateral-functioning kidneys during the administration of cisplatin-based chemotherapy for advanced urothelial carcinoma. METHODS: We retrospectively analyzed 244 advanced urothelial carcinoma patients treated with cisplatin-based chemotherapy between 2004 and 2010 at 17 institutes in Japan. The 24 h creatinine clearance, Cockcroft-Gault formula, and estimated glomerular filtration rate equation (eGFR), were compared before all chemotherapies. The urinary tract function status was determined based on the data of nephroureterectomy, hydronephrosis, and relief of upper urinary tract obstruction. A total of 244 patients were divided into four groups according to their urinary tract functioning status and eGFR results, including bilateral-functioning kidneys with pretreatment eGFR ≥60 mL/min/1.73 m2 group (n = 83, 34.0%); a solitary-functioning kidney with pretreatment eGFR ≥60 mL/min/1.73 m2 group (n = 36, 14.8%); bilateral-functioning kidneys with pretreatment eGFR < 60 mL/min/1.73 m2 group (n = 45, 18.4%); and a solitary-functioning kidney with pretreatment eGFR < 60 mL/min/1.73 m2 group (n = 80, 32.8%). RESULTS: The prevalence of nephrotoxicity with impaired eGFR of > 10% and 30% from baseline in the post-third-course of chemotherapy was significantly higher in patients with bilateral-functioning kidneys than in those with a solitary-functioning kidney, among patients with pretreatment eGFR < 60 mL/min/1.73 m2 (p = 0.023 and p = 0.026). During all courses of chemotherapy, the prevalence of nephrotoxicity with impaired eGFR of > 20% from baseline were significantly higher in patients with bilateral-functioning kidneys than those with a solitary-functioning kidney among patients with pretreatment eGFR < 60 mL/min/1.73 m2 (p = 0.034), whereas no significant difference was observed among patients with pretreatment eGFR ≥60 mL/min/1.73 m2. CONCLUSIONS: The results suggest that cisplatin-based chemotherapy may have more nephrotoxicity in patients with bilateral-functioning kidneys than in those with a solitary-functioning kidney.