The present study is an observational retrospective national register-based cohort study with long-term follow up of patients with mild traumatic brain injury from 2008-2012 in Denmark. Patients aged 18-60 years diagnosed with concussion from 2003-2007 in the national patient register will be included in the study. Data will be retrieved from several national databases, including the DREAM database containing data on social benefits and reimbursements. Primary outcome is return to work and secondary outcome are sickness absence, long-term sickness absence and disability pension.