BACKGROUND Despite advances in the treatment of abdominal injuries in patients with trauma, it remains a major public health problem worldwide. Evaluation of hazard ratio (HR) of 90-day mortality in intensive care unit (ICU) patients with abdominal injuries compare with head injuries in trauma patients and non-trauma surgical ICU patients. METHODS This single-center, prospective cohort study was conducted on 400 patients admitted to the ICU between 2018 and 2019 due to trauma or surgery in Hamadan, Iran. The main outcome was mortality at 90-day after ICU admission. Cox proportional hazards models were used to determine the HR and 95% confidence interval (CI) for 90-day mortality. RESULTS The 90-day mortality was 21.9% in abdominal injuries patients. According to multivariate Cox regression, the expected hazard mortality was 2.758 times higher in patients with abdominal injuries compared to non-trauma patients (HR: 2.758, 95% CI: 1.077-7.063, P=0.034). About more than 50% of all deaths in the abdominal and head trauma groups occurred within 20 days after admission. Mean time to death was 27.85±20.1, 30.27±18.22 and 31.43±26.24 days for abdominal-trauma, surgical-ICU, and head-trauma groups, respectively. CONCLUSIONS Difficulty in accurate diagnosis due to the complex physiological variability of abdominal trauma, less obvious clinical symptoms in blunt abdominal injuries, multi-organ dysfunction in abdominal injuries, failure to provide timely acute care, as well as different treatment methods all account for the high 90-day mortality rate in abdominal-trauma patients. Therefore, these patients need a multidisciplinary team to care for them both in the ICU and afterwards in the general ward.