Objective To investigate the correlation between optic nerve sheath diameter (ONSD) on computed tomography (CT) and intracranial pressure (ICP) in patients with acute severe traumatic brain injury after craniotomy, and to assess the performance of ONSD in predicting ICP.Methods A retrospective analysis was performed on the clinical data of 48 patients with acute severe traumatic brain injury. Thin-slice head CT reconstruction was used to measure the retrobulbar ONSD, and ICP was monitored using an invasive ICP sensor. According to the surgical procedure, these patients were divided into craniotomy group and ICP group. Linear and logistic regression methods were used to determine the correlation between ONSD and ICP and the performance of ONSD in predicting ICP.Results The 48 patients had a mean ONSD of 6.6 mm (SD 0.54) and a mean ICP of 12 mmHg (SD 6.5). There was a significant linear correlation between ONSD and ICP in the craniotomy group (P<0.001); ONSD had an area under the receiver operating characteristic curve of 0.964, and with a cut-off value of 7.1 mm, ONSD had a sensitivity of 100% and a specificity of 89%, suggesting that ONSD had a high performance in predicting ICP. But in the ICP group, there was no significant correlation between ONSD and ICP.Conclusions In patients with acute severe traumatic brain injury after craniotomy, ONSD is significantly correlated with ICP; ONSD >7.1 mm is predictive of ICP >20 mmHg, thus providing an important reference for these patients.