Aim To investigate age‐related mortality risk following traumatic brain injury (TBI). Methods Review of 2545 consecutive discharges from three metropolitan rehabilitation centres in New South Wales, between 1 January 1990 and 1 October 2007. Survival status was censored on 1 October 2009. Between‐group differences were assessed for older/younger patients. Multivariate Cox hazard regression was used to evaluate age‐related mortality risk. Crude mortality rates, standardised mortality ratios and cause of death data were derived for each age decade. Results After controlling for known mortality risk factors, older patients were three times more likely to die than younger patients. Crude mortality rates increased exponentially with advancing age. However, when compared to normative population data, younger adults with TBI (<50 years) had the highest risk of death relative to their non‐injured peers. Conclusions Crude mortality rates, which do not account for the naturally increasing rate of death associated with ageing, artificially inflate estimates of age‐related mortality risk following TBI.