OBJECTIVE: The incidence, associated injury pattern, diagnostic factors, risk for adverse outcome, and efficacy of anticoagulant therapy in the setting of blunt and carotid injury (BCI) were evaluated. SUMMARY BACKGROUND DATA: Blunt carotid injury is considered uncommon. The authors believe that it is underdiagnosed. Outcome is thought to be compromised by diagnostic delay. If delay in diagnosis is important, it is implied that therapy is effective. Although anticoagulation is the most frequently used therapy, efficacy has not been proven. METHODS: Patients with BCI were identified from the registry of a level I trauma center during an 11-year period (ending September 1995). Neurologic examinations and outcomes, brain computed tomography (CT) results, angiographic findings, risk factors, and heparin therapy were evaluated. RESULTS: Sixty-seven patients with 87 BCIs were treated. Thirty-four percent were diagnosed by incompatible neurologic and CT findings, 43% by new onset of neurologic deficits, and 23% by physical examination (neck injury, Horner's syndrome). There were 54 intimal dissections, 11 pseudoaneurysms, 17 thromboses, 4 carotid cavernous fistulas, and 1 transected internal carotid artery. Thirty-nine patients had follow-up angiograms. Mortality rate was 31%. Of 46 survivors, 63% had good neurologic outcomes, 17% moderate, and 20% bad. Logistic regression analysis demonstrated heparin therapy to be associated independently with survival (p < 0.02) and improvement in neurologic outcome (p < 0.01). CONCLUSIONS: Blunt carotid injury is more common than appreciated, seen in 0.67% of patients admitted after motor vehicle accidents. Therapy with heparin is highly efficacious, significantly reducing neurologic morbidity and mortality. Heparin therapy, when instituted before onset of symptoms, ameliorates neurologic deterioration. Liberal screening, leading to earlier diagnosis, would improve outcome.