Objective To investigate mortality rate in a population of adults admitted to hospital with mild head injury (MHI) 15 years later.

Design A prospective case control, record linkage study.

Participants 2428 adults with MHI and an equal number of community controls (CC) were case-matched for age, gender and social deprivation. A further control group admitted with a non-head injury was in addition matched for duration of hospital admission. Controls with a history of head injury prior to study entry were excluded.

Main outcome measures Death or survival 15 years poststudy entry.

Results Mortality per 1000 per year after MHI (24.49; 95% CI 23.21 to 25.79) was higher than in CC (13.34; 95% CI 12.29 to 14.44; p<0.0001) or ‘other injury’ controls (OIC) (19.63; 95% CI 18.43 to 20.87; p<0.0001). Age at injury was important: younger adults (15–54 years) with MHI had a 4.2-fold greater risk of death than CC; in adults aged over 54, the risk was 1.4 times higher. Gender and social deprivation showed a similar association with death in the MHI and control groups. Repeated head injury was a risk factor for death in the MHI group. The frequency of hospital admission with systemic disease preinjury and postinjury was higher in both injury groups than in CC and higher in MHI than OIC. Prospective data in the MHI group suggest an association between preinjury lifestyle and mortality. Causes of death after MHI were similar to those of the control groups.

Conclusions Adults hospitalised with MHI had greater risk of death in the following 15 years than matched controls. The extent to which lifestyle and potential chronic changes in neuropathology explain these findings is unclear. Lifestyle factors do contribute to risk of death after MHI and this finding has implications for lifestyle management interventions.