BACKGROUND: Major extracranial injury (MEI) is common in traumatic brain injury (TBI) patients, but the effect on outcome is controversial. OBJECTIVE: To assess the prognostic value of MEI on mortality after TBI in an individual patient data meta-analysis of 3 observational TBI studies (International Mission on Prognosis and Clinical Trial Design in TBI [IMPACT]), a randomized controlled trial (Corticosteroid Randomization After Significant Head Injury [CRASH]), and a trauma registry (Trauma Audit and Research Network [TARN]). METHODS: MEI (extracranial injury with an Abbreviated Injury Scale ≥ 3 or requiring hospital admission) was related to mortality with logistic regression analysis, adjusted for age, Glasgow Coma Scale motor score, and pupil reactivity and stratified by TBI severity. We pooled odds ratios (ORs) with random-effects meta-analysis. RESULTS: We included 39,274 patients. Mortality was 25%, and 32% had MEI. MEI was a strong predictor for mortality in TARN, with adjusted odds ratios of 2.81 (95% confidence interval [CI], 2.44-3.23) in mild, 2.18 (95% CI, 1.80-2.65) in moderate, and 2.14 (95% CI, 1.95-2.35) in severe TBI patients. The prognostic effect was smaller in IMPACT and CRASH, with pooled adjusted odds ratios of 2.14 (95% CI, 0.93-4.91) in mild, 1.46 (95% CI, 1.14-1.85) in moderate, and 1.18 (95% CI, 1.03-1.55) in severe TBI. When patients who died within 6 hours after injury were excluded from TARN, the effect of MEI was comparable with IMPACT and CRASH. CONCLUSION: MEI is an important prognostic factor for mortality in TBI patients. However, the effect varies by population, which explains the controversy in the literature. The strength of the effect is smaller in patients with more severe brain injury and depends on time of inclusion in a study.