Objective: To record and classify mechanisms of injury and injury severity score (ISS) in trauma patients admitted to the largest trauma center in Southern Iran.Methods: This was a prospective cross-sectional study including all the patients who were admitted to Nemazee hospital from 2009 to 2010. We recorded the trauma injury information of 1217 patients who were admitted to of emergency room of the Nemazee hospital during a 13-months period by means of a standard questionnaire. ISS was then obtained for every single patient.Results: The mean age of patients was 26.6 ± 15.1 (range 1–95) years. The commonest type of trauma including 279 cases (22.9%) was car accident and the least resulted from shotgun injuries in 13 (1.1%) patients. The lowest ISS was due to assault multiple blunt traumas and the highest ISS resulted from shotgun injury. The mean ISS was about 6.3 ± 1.8 (range 1-66). Overall, 86 patients had scores above 17 (7.1%). A total of 69 male patients (7.5%) compared to 17 females (5.7%) had severe injury (ISS>17). Trauma injuries were significantly more severe in males compared to females (p=0.014). In the sunny and hot seasons total number of patient was higher. The mean ISS was highest in during spring (p<0.001).Conclusion: In Shiraz, most of the trauma injuries are occurred during summer and hot weather. Men have greater number of injuries and higher ISS compared to women. The lowest ISS was due to assault multiple blunt trauma and the highest ISS was caused by shotgun injury, and car accident was the commonest cause of trauma with head and neck being the most frequent sites in our patients.