Background Head injuries are considered as a silent epidemic due to the high incidence rate throughout the world. The main cause of morbidity and mortality in patients with head injury is cerebral edema which is defined as abnormal fluid accumulation in the brain parenchyma. Mannitol is a hyperosmolar solution given to reduce fluid volume in the brain. Increased high intracranial pressure can affect prognosis and can be evaluated by assessing clinical outcomes in patients with severe traumatic brain injury using the Glasgow Outcome Discharge Scale (GODS) instrument. Methods Observational analytical study with a cross sectional design on 50 patients with severe traumatic brain injury at dr. Zainoel Abidin General Hospital Banda Aceh to determine the effect of mannitol use on the clinical outcomes of severe traumatic brain injury patients which used t test analysis. Results The mean value of the group that received mannitol had a higher GODS score than the group that did not receive mannitol. The results of the T test between groups obtained a p value of 0.000 which is smaller than 0.05, so it can be concluded that the use of mannitol has an effect on the GODS score in Severe traumatic brain injury patients. The results showed that the mean GODS value in patients who received mannitol was higher than those who did not receive mannitol. Conclusion This concludes that the administration of mannitol is effective in improving the clinical outcomes of patients with severe traumatic brain injury at dr. Zainoel Abidin General Hospital Banda Aceh.