Swelling in one or both kidneys due to a backup of urine.

Hydronephrosis can be caused by a blockage in the tubes that drain urine from the kidneys. It also can happen due to a difference present at birth that prevents urine from draining properly. In some people, hydronephrosis causes kidney damage over time.

Hydronephrosis often causes no symptoms. When symptoms happen, they can include painful urination, a need to urinate that is urgent or happens often, upset stomach, vomiting, fever, and failure to thrive in infants.

Hydronephrosis treatment depends on the condition's cause and how bad the symptoms are. Options can include medicine, a process to drain urine or surgery. In some people, mild hydronephrosis goes away on its own in time.