Background: A conceptual model for vulnerable populations research rel
ates resource availability and relative risk to health status. The mod
el has a population-based focus that places responsibility for the col
lective health status of its citizens with the community. Vulnerable p
opulations are social groups who experience limited resources and cons
equent high relative risk for morbidity and premature mortality. There
is considerable research evidence to support the major relationships
in the model. Conceptual links that need additional research are ident
ified. Conclusions: The implications for research include a variety of
methodological problems related to recruiting and retaining participa
nts, instrumentation, and data collection. Research designs are needed
that move beyond descriptive and epidemiological approaches to interv
entional and outcome studies. Ethical considerations take on special s
ignificance with vulnerable populations.