Glasgow coma scale was first defined in 1974. It was designed as a unified scoring system for assessing a patient’s conscious state. During the four decades of use, several versions of assessment were developed. Studies show that errors in assessment, especially for inexperienced examiners, are common. The scale is composed of three tests: eye opening, verbal response and best motor response. A patient’s eye opening is scored by testing if the patient’s eyes open spontaneously, after a verbal command or after a pain stimulus. In verbal response, we check if the patient’s speech is oriented in time and space, confused, consists of improper words or consists of only incomprehensible sounds. In best motor response, we look for the best motor response of a flexible limb, preferably upper limbs. The instructions to the patient must be clear. If the patient fails to follow these instructions, we proceed with painful stimulus. If the patient moves his hand above his clavicle, we speak of a localizing response. If his upper limb only flexes in the elbow, but the hand does not pass the clavicle, then we score this as a normal flexion. The motor response can also be seen as an abnormal flexion or extension of the extremities. In each test we must consider the circumstances that can affect the final score, such as intubation, the use of anesthesia and sedatives, facial, spinal or other injuries.