Sarcopenia is strongly associated with poor outcomes and mortality following injury among the geriatric population. Diagnosis using psoas area is most common but may be unavailable given limited radiographic evaluation following low-impact injuries. Masseter area has recently been identified as an available alternative and associated with 2-year mortality following injury. We sought to validate this measure and its association with early mortality following severe traumatic brain injury (sTBI) using a retrospective analysis of all geriatric trauma patients with sTBI admitted from 2011-2016 to our trauma center. Admission Glasgow Coma Scale (GCS) score ≤8 was used to identify sTBI. Bilateral masseter area was measured 2 cm below the zygomatic arch and the mean used for analysis. Sarcopenia was defined as mean masseter area one standard deviation or less from the sex-based mean. Multivariate models with logistic regression and Cox proportional hazards test followed univariate analysis. Kaplan-Meier survival curves were generated and evaluated by log rank. The primary outcome of interest was 30-day mortality. A total of 108 patients were identified for inclusion. Twenty-five patients, 16 male and nine female, had sarcopenia with mean masseter areas of 2.81 ± 0.45 cm2 and 2.24 ± 0.42 cm2, respectively. Patients with sarcopenia had significantly increased rates of 30-day mortality (80.0% vs. 50.6%; p = 0.01). Sarcopenia (odds ratio [OR], 2.95; 95% confidence interval [CI] 1.03-8.49) and decreasing masseter area were significantly associated with 30-day mortality (OR, 0.66; 95% CI 0.46-0.95) in multivariate modeling. Masseter area is a readily available and objective measure to determine sarcopenia, which is significantly associated with in-creased 30-day mortality following sTBI.