Spontaneous urinoma is a urological entity that can be complicated by a retroperitoneal abscess. Urinoma can be iatrogenic, traumatic, or can be caused by obstructive uropathy. We report two cases of spontaneous urinomas, describing a not previously published cause of urinoma: pyeloureteritis. (I) A 55-year-old Caucasian female started with intense left-sided flank pain for 3 days. CT scan revealed a voluminous retroperitoneal abscess, which extended through the posterior pararenal space and the left lumbar paravertebral musculature. (II) A 48-year-old Caucasian male presented with constitutional symptoms over the previous 2 months and investigations showed a voluminous urinoma and marked pyeloureteritis findings on CT scan. Both patients were managed by endoscopic placement of a double-J stent and drainage of the collection (open and percutaneous approach, respectively). Urinoma was confirmed by fluid biochemical analysis, which demonstrated that fluid creatinine was markedly raised as compared to the serum creatinine. Urinoma in the absence of obstruction or trauma is rare. These two case reports highlight one of the conditions leading to urinoma and the management of retroperitoneal abscess. Pyeloureteritis is a cause of spontaneous urinoma and it should be considered in the lack of another obstructive cause.