We aimed to validate a severity grading score (SGS) system for predicting the course of disease and fatality in Crimean-Congo hemorrhagic fever (CCHF). This SGS was established using several variables that were assumed to be associated with mortality and had clinical importance. We included patients diagnosed with CCHF from different centers. Patients who had symptoms of CCHF for <5 days were included. The patients were grouped into three categories according to mortality risk. An SGS ≤4 showed no association with mortality [n = 323 (79.9 % of the total study population), and all survived]. An SGS between 5 and 8 points was classified into the intermediate risk group (20 %), and 14 of 70 patients in this group died. An SGS ≥9 was classified as the high risk of mortality group and 11 of 11 patients in this group died (p = 0.001). The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for an SGS >9 points at admission were 96, 100, 97, 100, and 44 %, respectively. This SGS system may help appropriate the triage of patients, decrease the cost of treatment, and improve the functionality of healthcare staff. The present study is the first investigation about the validation of an SGS system in patients with CCHF.