With the use of ultrasound, most cases are found long before birth. After birth, signs in infants and children are:
- abdominal mass
- urinary tract infection with fever
- flank pain (pain in the upper abdomen or back, mostly with fluid intake)
- kidney stones
- bloody urine
- poor growth in infants
UPJ obstruction may also cause pain without an infection.
Some cases of UPJ obstruction are not clear. Urine may drain normally at times, and at other times be blocked. This causes pain that comes and goes. The general belief is that most children are not in pain unless the urine becomes infected or the blockage gets worse.