INTRODUCTION: To evaluate the prognostic value of optic nerve sheath diameter (ONSD) measured on the initial brain computed tomography (CT) scan for intensive care unit (ICU) mortality in severe traumatic brain injury (TBI) patients. METHODS: A prospective observational study of all severe TBI patients admitted to a neurosurgical ICU (10-month period). Demographic and clinical data, and brain CT scan results were recorded. ONSD for each eye was measured on the initial CT scan. The group of ICU survivors was compared to non-survivors. Glasgow Outcome Scale (GOS) was evaluated 6 months after ICU discharge. RESULTS: 77 patients were included (age: 43 +/- 18; 81% males; mean Injury Severity Score: 35 +/- 15; ICU mortality: 28.5% [n=22]). Mean ONSD on the initial brain CT scan was 7.8 +/- 0.1 mm in non-survivors vs. 6.8 +/- 0.1 mm in survivors (p<0.001). The operative value of ONSD was a good predictor of mortality (area under the curve [AUC]: 0.805). An ONSD cut-off [greater than or equal to] 7.3 had a sensitivity of 86.4% and a specificity of 74.6% and was independently associated with mortality in this population (adjusted odds ratio [AOR] [95% confidence interval]: 22.7 [3.2-159.6], p=0.002). There was a relationship between initial ONSD values and 6-month GOS (p=0.03). CONCLUSIONS: ONSD measured on the initial brain CT scan is independently associated with ICU mortality rate (when [greater than or equal to]7.3 mm) in severe TBI patients.