Driven by social, economic, academic and technological forces, the new field of E-health has been developing quickly in recent years. Many E-health applications are Internet-based and therefore have the potential to help people throughout the world. However, this high dependence on the Internet also raises sobering questions about a health digital divide, i.e. unequal access and use as well as unequal rights to gain benefits of online information among health consumers. In this paper, we discuss social, cultural and economic factors which shape a research agenda for examining health digital divide issues. These factors are derived by means of a literature review. Future research questions include how to solve the discrepancies between health digital divide and digital divide among the general population, what is the role of content prejudice in health digital divide, and what is the status quo of health digital divide in developing countries, et al.