Urinomas can occur after renal trauma or perforation of the collecting system during an endosurgical procedure. However, spontaneous urinomas are very rare. Here we report a case of a spontaneous perinephric urinoma following the removal of a Foley catheter in an 18-year-old girl with acute kidney injury caused by septic shock. The patient had been treated for septic shock, acute kidney injury, and acute respiratory distress syndrome, and had a Foley catheter in place for seven days. After Foley catheter removal, the patient complained of consistent voiding difficulty. An abdominal computed tomography scan showed a large amount of left perinephric fluid, and the aspirated fluid included urothelial cells, confirming the diagnosis of a urinoma. The urinoma was successfully treated by insertion of a double-J stent into the left ureter. This report discusses the available literature on urinomas, and their clinical features, diagnosis, and treatment.