A ureteral cyst is a congenital developmental abnormality, a developmental defect in the part of the ureter that enters the bladder, resulting in a very small ureteral opening that forms a cystic bag in the bladder like a balloon as it is pushed by the urine stream. Some people have a combination of other developmental abnormalities, commonly a duplicated pelvic ureter with two sets of urinary ducts on one side instead of one set of urinary ducts as in the general population. This condition is most often seen in children and often presents with recurrent urinary tract infections, hydronephrosis, and even renal impairment. As urine accumulates in the distal capsule of the duct, some will form stones. In adults, most cysts are solitary, and duplication of the pelvic ureter is rare. When the cyst is large, it may block the opening of the bladder urethra and interfere with urination. When combined with stones or infection, it may cause urinary urgency, painful urination and frequent urination. Ureteral cysts are usually divided into four types. Treatment depends on the presence of symptoms, infection, stones, hydronephrosis and other conditions. Currently, they are mostly treated with minimally invasive surgery. There are various methods, which can be as simple as enlarging the tiny opening or cutting the bulging cyst, removing the stone at the same time if it is combined with a stone, and some people may need to redesign the ureteral opening in the bladder to prevent urinary reflux.