Purpose: Fear of genetic discrimination might deter participation in research or therapy. This is a major impetus for laws limiting insurers' use of genetic information, yet there is little information about the extent of this fear in the general population and how it varies by social factors. Methods: This study measures concern about insurance problems relating to genetic testing, as part of primary-care screening for hereditary hemochromatosis (iron overload). Data come from a multiethnic, primary care-based survey of 86,859 adults in five field centers in the United States (AL, CA, DC, HI, OR), and one in Canada (Ontario). Logistic regression was used to model the probability of agreeing to the question "Genetic testing is not a good idea because you might have trouble getting or keeping your insurance." Results: Overall, 40.0% of participants agreed. Adjusting for other characteristics, African Americans and Asians were much less likely (OR = 0.52 and 0.39), and Hispanics were more likely (OR = 1.124), than Caucasians to express concern about insurance discrimination. Participants under 65 years old, US residents, and those without a high school diploma were substantially more likely to be concerned (ORs ranging from 1.4-1.6), as were participants with lower mental health scores. Education showed a nonlinear relationship, with significantly higher concern among both those with less than a high school education and those with a college degree, compared to high school graduates. Conclusions: Concern about genetic discrimination varies substantially by race and other demographic factors and by nationality. One possible explanation for lower concern about Canadians and by people over 64 is that both groups are covered by social insurance for health care (Medicare). However, US residents in states with some legal protections against genetic discrimination had more, not less, concern than either Canadians or US residents in states with no legal protections.