Blunt renal trauma is managed conservatively in children in the vast majority of cases. Grade IV renal injury is also generally managed non-operatively although occasionally intervention is needed for a urinoma that fails to settle. These authors retrospectively looked at the medical records of 26 children presenting to their centre over the course of 18 years with grade IV injury to the kidney. They were keen to see if they could predict which children needed intervention. Twenty-six patients (20 boys, 6 girls – mean age 11 years), sustained injury from: a road traffic accident (12); a fall (13); violence (one). Out of the patients four had immediate haemostatic intervention in the form of surgery (one) and angiointervention (three). Transfusion was needed in 14 and gross haematuria occurred in 21. The mean size of the perinephric haematoma was 2.3cm. Of the 22 initially managed conservatively, eight had further urological intervention because of large urinoma, secondary haemostatic instability or other symptoms. Five had ureteral stents with or without percutaneous drainage of the urinoma. Three were treated with nephrostomy (two) or renorrhaphy (one). The authors conclude that most patients receive intervention four to eight days after trauma and that predictive factors for this included need for transfusion, urinomas >2.2cm in size, an antero-medial laceration on CT (occurring in nine patients) and intravascular contrast extravasation. The authors also suggest that follow-up imaging should occur four to five days after the initial injury.