['The inferior vena cava (IVC) collapses with shock but may also be collapsed in volume-depleted patients in the absence of shock. The speed and availability of computed tomography (CT) make IVC measurement an attractive diagnostic modality for shock. The purpose of this study was to determine if IVC size following injury is associated with shock.', 'Retrospective data were collected on 272 trauma patients admitted to an adult trauma center from January 1 to December 31, 2012. Patients who met the highest-level activation criteria and underwent an abdominal CT scan during their initial resuscitation were included. All images were reviewed by two attending radiologists, and concordance was assessed using the Pearson correlation coefficient. The transverse (T) and anteroposterior (AP) diameters of the IVC were measured to calculate a T/AP ratio. Analysis of variance and χ were used to assess for a relationship between this ratio and various indices of shock.', 'The mean (SD) age of the study cohort was 50 (21) years, mean (SD) Injury Severity Score (ISS) was 14 (9), 74% were male, and 96% sustained blunt trauma. The overall mean (SD) T/AP ratio was 1.81 (0.68). Patients with a shock index greater than 0.7 were significantly younger (43 [20] years vs. 55 [21] years, p < 0.0001), had a significantly lower mean arterial pressure (88 [15] mm Hg vs. 103 [18] mm Hg, p < 0.0001), and were more likely to be intubated (56% vs. 24%, p < 0.0001). However, IVC T/AP ratio was not significantly different among the cohort. Similarly, there was no association between IVC size and the need for urgent operation, angiography, emergent transfusion, hospital length of stay, or mortality.'] Is inferior vena cava size associated with shock following injury?