This study examined the extent to which individualism-collectivism moderates the relative effects of agency control beliefs (i.e., self-efficacy), social norms (i.e., subjective norms), and risk perception (perceived vulnerability and perceived severity) on behavioral intention to engage in self-protection behavior in the context of the H1N1 flu pandemic. Using multistage stratified sampling, the present study sampled people from the US (n = 399) and Korea (n = 500), two countries that have been found to be prototypical of individualistic and collectivistic national cultures, respectively. Consistent with the contrast between individualism and collectivism, the results of moderated regression analyses showed that intrapersonal control beliefs (i.e., self-efficacy) and risk perception (i.e., perceived severity) had stronger effects on behavioral intention in the American sample than in the Korean sample, whereas social norms (i.e., subjective norms) had a stronger predictive power for the Korean sample than for the American sample. Overall, the findings contribute to health and risk studies by specifying which aspects of risk perceptions or beliefs are affected by national culture and how this translates into cross-national variations in health risk behavioral intention.