In three genome wide association studies a single nucleotide polymorphism (SNP) in close proximity to the interleukin 28 B (IL-28B) gene, which encodes for the type III interferon lambda 3 (IFN-λ3), has been shown to be significantly associated with response to IFN-based therapy of chronic hepatitis C and with the natural course of acute hepatitis C [3–5]. Here, IFNL3 is linked to hepatitis C virus infection.