A 28-year-old woman suffered from bilateral flank pain recently. She had a history of repeat urinary tract infection for more than 5 years. Physical examination revealed no abnormalities and laboratory workup showed urine leukocytosis. Intravenous urography demonstrated four collecting systems and four renal shadows (Fig. 1A). Voiding cystourethrography showed no vesicoureteric reflux. MRI confirmed four separate kidneys (Fig. 1B) with four collecting systems and individual renal capsules (Fig. 1C), indicating supernumerary kidneys rather than duplication. Bilateral hydronephrosis at lower positioned kidneys were noted. Under the diagnosis of bilateral supernumerary kidney with repeat infection, the patient received antibiotic treatment (250 mg b.i.d, ciprofloxacin tablet) for seven days. The symptoms subsided and close follow up was provided at the outpatient department.