Hepatitis B virus (HBV) infection and its associated liver diseases have characteristics of familial clustering in China. However, the reasons for this are not understood fully. To address this issue, the prevalence HBV infection and the characteristics of unfavorable prognoses in clustering of infection in families in northwest China were investigated. Families with clustering of infection and unfavorable prognoses were enrolled, and general information and serum samples were collected. The clinical features and sequelae of HBV infection were compared among the blood relatives (including the first-, second-, and third-degree blood relatives) and spouses using the chi-square test or Fisher's exact test. A total of 102 clusterings of infection families with unfavorable prognoses were interviewed. In the first-, second-, and third-degree blood relatives and spouses, the prevalences of cirrhosis of the liver were 29.2%, 11.9%, and 8.7%, respectively, while those of hepatocellular carcinoma (HCC) were 21.8%, 1.4%, and 4.3%, respectively (P < 0.05). The mean ages of the onset of cirrhosis of the liver in the first-, second-, and third-degree blood relatives and spouses were 57 ± 9.91, 47 ± 9.96, 38 ± 10.35, and 57 ± 8.49 years, respectively, while the mean ages of the onset of HCC were 60 ± 7.92, 49 ± 8.57, 41 ± 3.54, and 50 ± 0 years, respectively, (P < 0.05). The first-, second-, and third-degree blood relatives from clustering of infection in families with unfavorable prognoses had prevalences of cirrhosis or HCC in descending order of relationship. The findings suggest that genetic factors may be associated with a familial tendency for cirrhosis of the liver and HCC. J Med. Virol. 85:1893–1899, 2013. © 2013 Wiley Periodicals, Inc.