Introduction: This present study focuses on the findings of clinical trials that have revealed unsatisfactory results and mortality escalation rates of patients suffering from serious traumatic brain injuries (TBI). Aim: The main objective of this research was to investigate whether hyperglycaemia is a significant indicator of mortality in patients with the diagnosis of severe TBI. Methods: The research was performed using meta-analysis. The research material was collected throughout PubMed, Cochrane, NCBI, and Google Scholar from 2010 to 2020. Results: The research subjects were patients with TBI, proven to have hyperglycaemia on admission (random blood sugar evaluation > 200 mg/dl on arrival at the emergency department), with or without a history of DM (HbA1C evaluation ≥ 6.5%), a Glasgow Coma Scale score ≤ 8, and aged 0 - 100 years. The pooled risk ratio (RR) for mortality in severe TBI with hyperglycaemia on admission was 2.39. The evidence of mortality appeared significantly greater in patients with TBI with hyperglycaemia on admission than in those with normal blood glucose levels (RR = 2.39, p < 0.00001). The pooled RR had wide heterogeneity (I2 = 0.87), so the random-effect model was used. Conclusion: Hyperglycaemia on admission is often associated with unsatisfactory clinical outcomes and greater mortality.