The aim of this study was to determine the association between bicycle helmet use in adults (16 years and older) and traumatic brain injury (TBI) in emergency departments (EDs) in the Netherlands.The conducted research was a retrospective case-control study in patients aged 16 years and older who sustained a bicycle accident and therefore visited the EDs of participating hospitals throughout 2016. Cases were patients with TBI; controls were patients without TBI but with other trauma. Exposure was defined as helmet wearing during the accident. In total, 2133 patients were included in the study, 361 case patients and 1772 controls. Within the TBI group (cases) 3.9% of patients wore a helmet compared with 7.7% of patients in the control (non-head injury) group (odds ratio [OR] 0.49, 95% confidence interval [CI]: 0.28-0.86). No difference in helmet wearing was observed in patients who sustained accidents that involved motorized vehicles (OR 0.91; 95% CI: 0.29-2.83). In conclusion, adult patients (?16 years of age) with TBI had a significantly lower odds of wearing a bicycle helmet than adult patients with other trauma, adding more evidence that wearing a bicycle helmet effectively protects against TBI.