Purpose: Non-invasive blood pressure measurement is widely used as a pre-hospital triage tool for blunt trauma patients. However, scant data exits for using the mean arterial pressure (MAP), compared to the systolic blood pressure, as a guiding index. The aim of this study was to determine the association between adverse outcomes and mean arterial pressure (MAP) and to exhibit the therapeutic range of the MAP in adult blunt trauma patients. Methods: The electronic medical records for all trauma patients in a single hospital from January 2010 to September 2012 were retrospectively reviewed. Patients below 17 years of age, patients with penetrating injuries, and patients with serious head trauma (injuries containing any skull fractures or any intracranial hemorrhages) were excluded. Adverse outcomes were defined as one of the following: death in the Emergency Department (ED), admission via operating theater, admission to the intensive care unit, transfer to another hospital for emergency surgery, or discharge as hopeless. Results: There were 14,537 patients who met entry criteria. Adverse outcomes occurred for MAPs in range from 90 to 120 mmHg. Adverse outcomes were found, after adjusting for confounding variables, to occur increasingly as the MAP declined below 90 mmHg or rose above 120 mmHg. Conclusion: Not only lower but also higher mean arterial pressure is associated with increased adverse outcomes in adult blunt trauma patients. Thus, patients with a MAP above 120 mmHg should be considered as a special group requiring higher medical attention, just as those with a MAP below 90 mmHg are.