This report describes the case of a patient in her late teens with fragile X syndrome, developmental delay, and recurrent urinary tract infections who presented to the emergency department with a productive cough, weight loss, and being generally unwell over the past few weeks. She was found to have a firm, distended abdomen and, while being investigated for sepsis of unknown source, deteriorated rapidly and was intubated and ventilated in the intensive care unit (ICU). After multiple imaging studies, she was diagnosed with left ureteric rupture secondary to a left distal ureteric calculus, resulting in a urinoma in the left retroperitoneal space. An interventional radiology-guided drain was inserted to drain the urinoma, and a left nephrostomy and anterograde ureteric stent were inserted. Her condition improved after these interventions, and she was later extubated and discharged from the ICU to the general ward.