This study evaluates the efficacy of adjuvant cisternostomy (AC) versus decompressive craniectomy (DC) in managing severe traumatic brain injury (sTBI). A single-center retrospective analysis of consecutive sTBI patients treated with AC or DC alone (2018-2019) revealed that the AC group exhibited significantly lower intracranial pressure and higher Glasgow Coma Scale scores compared with the DC group (P < .05). Cerebrospinal fluid and serum analyses demonstrated reduced interleukin-1β and nerve fiber layer levels in the AC group. In addition, the AC group required lower mannitol dosages and showed fewer postoperative complications. Six-month follow-up indicated a statistically higher rate of good prognosis in the AC group (P < .05). These findings suggest that AC is superior to DC in reducing intracranial pressure, mitigating neurological damage, and improving clinical outcomes in sTBI patients.