Objectives: The objective of this study was to determine the incidence of olfactory dysfunction in workers following head injury in the work place, to define its relationship to the site, severity of injury and direction of force. The demographics of head injured workers were also assessed to determine whether those with olfactory loss were more likely to have sustained a cochleovestibular injury. Design: Retrospective case analysis. Setting: Tertiary referral university hospital in Toronto, Ontario. Participants: A total of 3438 consecutive patients referred from the Workplace Safety and Insurance Board (WSIB) in the province of Ontario who sustained a work-related head injury were assessed between 1987 and 2014. Main outcome measures: Olfactory and cochleovestibular dysfunction assessed by history, clinical examination and subjective and objective tests. Results: Olfactory dysfunction (OD) was identified in 413 of 3438 patients (12.0%) of which 321 were diagnosed with anosmia and 92 with hyposmia. In our series, injuries from a fall were the commonest cause for OD and a frontal or mid-face impact was more likely to result in OD than other regions (P = 0.0002). A loss of consciousness (LOC) of any duration correlated with OD. In those with olfactory dysfunction, an associated skull fracture occurred in 37.1% of patients and a CSF leak in 4.1%, which was significantly higher compared with those without OD(<0.0001). Patients with OD had a higher incidence of cochlear and vestibular loss (19.9% and 20.6%, respectively) compared with those without OD (14.3% and 17.1%, respectively). Conclusions: Post-traumatic olfactory dysfunction is more likely to occur in patients who experienced a moderate to severe head injury, LOC and more likely to result from a frontal or mid-face blow to the skull. Cochleovestibular dysfunction is likely to occur concurrently with olfactory dysfunction.