Background: Recent discovery of the Th17 pathway is providing new opportunities for understanding chronic immune-mediated diseases. The Th17 pathway has been historically associated with chronic inflammatory diseases such as psoriasis, multiple sclerosis, and rheumatoid arthritis. Among Th17 cytokines, pathogenic roles of IL-17A and IL-17F in asthma have been well described. Recently, the number of peripheral blood Th17 cells was found to correlate with disease severity in patients with atopic dermatitis (AD). This study aimed to investigate serum IL-17F levels in children with AD and to correlate this with severity of the disease. Methods: Enzyme-linked immunosorbent assay was used to measure IL-17F levels in the sera of 228 patients with AD and 62 control children. The SCORing Atopic Dermatitis (SCORAD) tool was used to determine the severity of disease. Results: The mean serum level of IL-17F in children with AD was significantly higher than that in the control group (p<0.05) Serum IL-17F levels were also higher in patients with severe AD than in those with mild AD (p<0.001), and IL-17F levels and SCORAD scores were positively correlated (p<0.05). Conclusions: Serum IL-17F level might be a useful marker in children with AD.