Crimean-Congo hemorrhagic fever (CCHF) is a potentially fatal disease affecting multiple organ systems. To determine the association between viral load and severity of CCHF infection, quantitative measurement of CCHF virus was performed using 1-step reverse-transcriptase polymerase chain reaction for 36 patients with CCHF infection. Viral loads ranged from 1.1x10(3) copies/mL to > or = 9.9x10(9) copies/mL. Nine (25%) of 36 patients died. In 8 of the 9 patients with fatal outcomes, viral loads were detected that were > or = 1x10(9) copies/mL, whereas in 25 of the 26 patients with nonfatal outcomes, viral loads were detected that were < 1x10(9) copies/mL (P<.001). A viral load > or = 1x10(9) RNA copies/mL can be considered to predict a fatal outcome with a positive predictive value of 80%, with 88.9% sensitivity and 92.6% specificity. We suggest that viral load is a measure of the severity of CCHF.