From December 2009 to May 2013, 16,854 patients with chronic hepatitis C were registered from 37 prefectures in Japan (median age: 60 years; 50.4 % male; 74.8 % IFN-naïve; HCV genotype [1 or 2]/viral load [high (≥5 log IU/mL) or low (<5 log IU/mL)]: 1/high = 58.2 %, 1/low = 5.2 %, 2/high = 27.3 %, 2/low = 7.5 %; 83.4 % treated with peginterferon-α and ribavirin). Here, IFNA1 is linked to chronic hepatitis C virus infection.