We investigated the role played by cytokines in the mortality of patients with Crimean-Congo hemorrhagic fever (CCHF). Serum levels of several cytokines were measured in 3 patients with fatal CCHF and in 27 patients with nonfatal CCHF. Levels of interleukin (IL)-6 (P< or = .001) and tumor necrosis factor (TNF)-alpha (P = .004) were significantly higher in patients with fatal CCHF than in patients with nonfatal CCHF, whereas levels of IL-10 were not significantly different between the 2 groups (P = .937). Disseminated intravascular coagulation (DIC) scores were also higher in the patients with fatal CCHF (P = .023). Levels of IL-6 and TNF-alpha were positively correlated with DIC scores, whereas levels of IL-10 were negatively correlated with DIC scores. In conclusion, these findings demonstrate that proinflammatory cytokines play a major role in the mortality of patients with CCHF.