For many decades, Vietnam had a well-structured public health service with extensive population coverage, with free care at government health facilities until 1989. Since then the country has been going through economic transition, including major changes to the health system. These include the reduction of financial support to public facilities and the introduction of user charges. Concern has been growing about the effect of these changes on access and affordability of health care, particularly for poor families. Using data from the Vietnam National Health Survey conducted in 2001-2002, the authors conducted a tracer study of people with diarrheal illness to examine equity in access to and use of health care and the financial burdens placed on patients in seeking care. The study found that children, the elderly, and the poorly educated were more likely to suffer from diarrhea; poor people often did not seek any care regardless of severity of illness, largely because they could not afford it. The opportunity cost due to lost income was also much greater for poor families. Several new policies have been developed in Vietnam to improve access to basic health care for the poor. However, the effects of such policies require close monitoring and remain to be evaluated.