A 238-day-old female infant (122 days of age corrected for prematurity, weight 4, 847 g) presented with macrohematuria. She was born at 23 weeks and3 days of pregnancy. Her birth weight was 492 g. Ultrasound revealeda 3×2 mm left ureteral stone and left hydronephrosis of grade I-II in the Society of Fetal Urology (SFU) Classification. She suffered from frequent vomiting and weight loss, and was treated with analgesics and rehydration. Eventually, left hydronephrosis was relieved, and she passed the stone at 271 days of age. The stone was 4×3×2 mm in size, and consisted of 98% calcium oxalate and2% calcium phosphate. No recurrent stone has been found during follow-up.