Background: Ultrasound assessment of optic nerve sheath diameter (ONSD) has been used as a promising tool to aid in the diagnosis of elevated intracranial pressure (ICP). Optic nerve sheath is contiguous with the dura matter surrounding the brain and contains cerebrospinal fluid, which allows transmission of pressure from the cranium. Objective: To determine the diagnostic accuracy of measurement of ONSD by using ocular ultrasonography to detect elevated ICP in patients with TBI in Emergency Department. Patients and methods: This prospective cross-sectional observational study that was carried out on 99 patients presented and admitted to Mansoura University Emergency Hospital with traumatic brain injury (TBI) over a year from June 2020 to June 2021. Results: The clinical features of raised ICP had low specificity (38%), positive predictive value (PPV) (61.7%), and accuracy (69%) for diagnosis of raised ICP with high significant statistical difference (62% vs 100%) towards group 2. The ONSD were much higher (P <0.01) in group 2 (6.493 ± 0.586 mm) than group 1 (3.93 ± 0.976 mm). The cutoff value of binocular mean ONSD for diagnosing raised ICP was > 5 mm with sensitivity of 100 %, specificity of 96%, and accuracy of 99%. The optimal cutoff value to predict mortality rate was >6.8 mm with modest sensitivity and accuracy. While the optimal value to predict unfavorable Glasgow Outcome Scale (GOS) was >6.05 mm with high sensitivity and accuracy. Conclusion: ONSD measurement via bedside ocular ultrasound is a useful, non-invasive method for early diagnosis of elevated ICP in adult patients with TBI in the Emergency Department.