Rationale:The duplex ureter is a common anomaly of urinary tract, but preoperative sonography, plain abdominal radiography, or nonenhanced computed tomography (CT) often overlooked it when involved with urinary tract obstruction. In this report, We present a rare case of left Y-shaped bifid ureter and both ureter of upper moiety and common stem were obstructed respectively by 2 calculi.Patient concerns:A 47-year-old woman was admitted due to 3-day history of left-sided loin pain and low-grade fever. The patient was diagnosed with right renal atrophy and 2 calculi of left ureter associated with severe left hydronephroureterosis, and underwent left percutaneous nephrostomy and left ureterolithotomy without identification of the upper calculus in left ureter in another hospital.Diagnoses:After transfer of the patient to our hospital, preoperative contrast-enhanced CT detected the left Y shaped bifid ureter and the calculus in upper moiety ureter.Interventions:The migrated calculus was extracted by left ureterolithotomy.Outcomes:The patient discharged uneventfully.Lessons:Contrast-enhanced CT should be recommended prior to any surgical procedures involved with upper urinary tract to exclude duplex ureter.