OBJECTIVE: We aimed to estimate from a societal perspective the 1-year and lifetime direct and indirect costs of traumatic brain injury (TBI) for New Zealand (NZ) in 2010 projected to 2020. METHODS: An incidence-based cost of illness model was developed using data from the Brain Injury Outcomes New Zealand in the Community Study. Details of TBI-related resource use during the first 12 months after injury were obtained for 725 cases using resource utilization information from participant surveys and medical records. Total costs are presented in US dollars year 2010 value. RESULTS: In 2010, 11,301 first-ever TBI cases were estimated to have occurred in NZ; total first-year cost of all new TBI cases was estimated to be US $47.9 million with total prevalence costs of US $101.4 million. The average cost per new TBI case during the first 12 months and over a lifetime was US $5,922 (95% confidence interval [CI] $4,777-$7,858), varying from US $4,636 (95% CI $3,756-$5,561) for mild cases to US $36,648 (95% CI $16,348-$65,350) for moderate/severe cases. Because of the unexpectedly large number of mild TBI cases (95% of all TBI cases), the total cost of treating these cases is nearly 3 times that of moderate/severe. The total lifetime cost of all TBI survivors in 2010 was US $146.5 million and is expected to increase to US $177.1 million in 2020. CONCLUSION: The results suggest that there is an urgent need to develop effective interventions to prevent both mild and moderate/severe TBI.