To investigate whether inferior vena cava (IVC) calibre on paediatric trauma computed tomography (CT) can help anticipate outcomes in children.The imaging and clinical records of 52 paediatric trauma admissions to the level 1 major trauma centre at St George's Hospital, London, UK, were retrospectively reviewed. The IVC dimensions, evidence of significant haemorrhage on CT, and the presence of components of the classical hypoperfusion complex, such as bowel and adrenal hyperenhancement, were recorded. Clinical data included observations at the time of admission and for the subsequent 48-hour period where available, blood gas results, length of stay, and mortality.There was a significant relationship between IVC dimensions in this cohort and the development of shock during the 24-hour admission period. IVC dimensions did not, however, reflect the haemodynamic status at the time of admission, and were not predictive of a longer hospital stay. There were no mortalities among the cases. A weak correlation was also seen with serum lactate, a finding that has also been seen in adults, but is of uncertain clinical significance.IVC calibre was found to be a more useful predictor of shock than heart rate or blood pressure, and may, therefore, prove to be a useful predictor of impending haemodynamic instability in children as it is in adults. Although the study was carried out at a busy unit, the numbers are acknowledged to be small and a larger study would be needed to validate these findings and identify whether there is any variation in the CT appearances between different age groups.