Background and Objectives:The Full Outline of Un-Responsiveness (FOUR) scale is a tool to assess the consciousness level in patients admitted to the Intensive Care Units (ICU). The validity and reliability of this scale can be affected by distorting factors, such as social, cultural, biological, and physiological conditions. This study aimed to evaluate the standardization of the FOUR scale to assess the consciousness level of the patients based on demographic characteristics in the Iranian population.Methods: This experimental cross-sectional study was conducted on 60 patients hospitalized in the ICU. The FOUR scale was used to determine the consciousness level of the patients. Reliability, internal consistency, as well as correlations between the scales were estimated using Cronbach's alpha and Spearman-Brown formula. The data were analyzed in SPSS software (version 16.0) (SPSS Inc., Chicago, Illinois, USA). A p-value less than 0.05 was considered statistically significant. Results:According to the results, the internal consistency values of the Glasgow Coma Scale (GCS) and FOUR scale were estimated at 0.943 and 0.889, respectively, using Cronbach's alpha. In addition, there was a significant correlation between the FOUR scale and GCS (r=0.948, P=0.001). Furthermore, the sum of sensitivity and specificity of the total score of the FOUR scale and GCS were obtained at 5 (sensitivity=0.72; specificity=31.43) and 7 (sensitivity=0.68; specificity=0.3714), respectively. In addition, the Area under the ROC Curve value in predicting in-hospital mortality for the FOUR scale was 0.491 (P=0.910 and 95% CI: 0.338-0.645), while it was obtained at 0.527 (P=0.725 and 95% CI: 0.374-0.679) for the GCS. Conclusion:The results revealed that the GCS could be used as a standard scale to assess the consciousness level of the patients. The FOUR scale and GCS have similar benefits, and the former is a valuable tool to assess the consciousness level due to the combination of eye and motor components. Therefore, GCS could be used as substitute for the FOUR scale.