Spontaneous rupture of renal pelvis with urinoma formation is relatively unusual. We experienced 3 cases of this phenomenon. The causes of peripelvic leakage were ureteral stone, ureteral tumor(transitional cell carcinoma) and bladder turn or(transitional cell carcinoma) with obstruction of the ureterovesical junction. Among these three cases, one patient presented with signs resembling the symptoms of peritonitis. Therefore, it is necessary to dfferentiate peripelvic extravasation from other disease entities of acute abdomen and to search for the underlying disease of this phenomenon carefully. We must be alert that this condition may also be caused by malignant ureteral obstruction.