Objective: The adherence of the physicians to guidelines in resuscitation of the patients is of great importance since it can predict the outcome. To evaluate the adherence of the physicians of our center in hydration of traumatic patients with crystalloids regarding the Advanced Trauma Life Support (ATLS) guidelines. Methods: We designed an algorithm obtained from ATLS guidelines using vital signs and status of bleeding of the traumatic patients to classify them. After categorizing the patients according to the algorithm, we evaluated the adherence of the physicians to the guideline in hydration of traumatic patients with crystalloids. Results: This is a cross-sectional study in which 998 traumatic patients who were admitted to the emergency ward of Rajaee trauma hospital were enrolled. Most of the patients were men (89.6%) and the most common causes of traumatic injuries were traffic accidents. Proper hydration was seen in only 14.7% of the patients. Most of the patients were overhydrated (85%) regarding both our algorithm and the patients’ base excess. Conclusion: The present study showed that the adherence of physicians in our center in resuscitation with crystalloid was low. Also, most of the traumatic patients were overhydrated with crystalloids. It is suggested that physicians retrain concerning the side effects of over hydration. In addition, we need a user friendly and more applicable guideline for hydration with crystalloids.