Trends in age-specific incidence rates from primary liver (excluding intrahepatic bile duct) cancers were examined, using the US Cancer Statistics database (1999-2009) with data from the National Program of Cancer Registries and the Surveillance, Epidemiology and End Results Program. The largest increase was for ages 55 to 64 years, but the rate for ages 45 to 54 years reached a plateau and showed a recent decline for ages 35 to 44 years, consistent with an impact of the epidemic of hepatitis C virus (HCV) infection which peaked in persons born from 1945 to 1965. Interpretation of trends, however, has been hampered by the lack of data on comorbid HCV infection from central cancer registries. Using a national mortality database with multiple causes of death for all US residents (1999-2010), the increase in the proportion of deaths from liver cancer with comorbid HCV infection also mentioned on the certificate was largest for the group aged 55 to 64 years. Death records are limited to decedents and underestimate comorbid HCV infection, but central cancer registries can use additional sources (such as administrative databases and reports from hospital registries) in interpreting trends in liver cancer incidence rates.