A social health insurance (SHI) program was implemented in Vietnam in 1992. Participation is compulsory for some groups, such as formal-sector workers and voluntary for other groups. In 2013, 68% of the total population was covered by SHI, with most enrollees from compulsory groups. Enrollment has remained low among persons whose enrollment is voluntary. As a result, households face financial risk due to high out-of-pocket payments for health care. The goal of this study is to identify willingness to pay (WTP) for the SHI scheme among persons whose enrollment is voluntary and to examine factors that influence their choice