Background: Trauma is a leading cause of morbidity and mortality among individuals under 40 and is the third main cause for death throughout the world. Objectives: This study was designed to compare our modified injury scoring systems with the current injury severity score (ISS) from the viewpoint of its predictive value to estimate the duration of hospitalization in trauma patients. Patients and Methods: This analytical cross-sectional study was performed at the general referral trauma center of Bandar-Abbas in southern Iran from March 2009 to March 2010. The study population consisted of all the trauma patients referred to the emergency department (ED). Demographic data, type and severity of injury, duration of admission, Glasgow coma scale (GCS), and revised trauma score (RTS) were recorded. The injury severity score (ISS) and NISS were calculated. The length of hospital stay was recorded during the patients follow-up and compared with ISS, NISS and modified injury scoring systems. Results: Five hundred eleven patients (446 males (87.3%) and 65 females (12.7%)) were enrolled in the study. The mean age was 22 ± 4.2 for males and 29.15 ± 3.8 for females. The modified NISS had a relatively strong correlation with the length of hospitalization (r = 0.79). The formula below explains the length of hospitalization according to MNISS score. Duration of hospitalization was 0.415 + (2.991) MNISS. Duration of hospitalization had a strong correlation with MISS (r = 0.805, R2: 0.65). Duration of hospitalization was 0.113 + (7.915) MISS. Conclusions: This new suggested scale shows a better value to predict patients’ length of hospital stay compared to ISS and NISS. However, future studies with larger sample sizes and more confounding factors such as prehospital procedures, intubation and other procedures during admission, should be designed to examine these scoring systems and confirm the results of our study.