The evaluation of acute emesis in a multiple-trauma paediatric patient with severe traumatic brain injury can present a difficult but not unusual problem in the rehabilitation unit. The differential diagnosis will be discussed in a paediatric case in which emesis was related to a urinoma, secondary to ureteropelvic disruption, compressing the duodenum. We present a case of a 6-year-old Caucasian girl with severe brain injury who developed emesis while in rehabilitation. An X-ray of the abdomen revealed a shadow over the right psoas. Subsequently mild compression of the duodenum was diagnosed by computerized tomography, and ultrasound demonstrated a large fluid collection inferior to the right kidney. A large volume of urine was drained and a catheter placed. Pyelogram revealed apparent disruption of the right ureteropelvic junction, which was confirmed intraoperatively. The kidney was removed secondary to severe parenchymal abnormalities. The emesis subsequently resolved. Differential diagnosis of acute onset of emesis in the paediatric brain-injured patient should include a careful search for underlying previously unrecognized problems.