Background: The use of race as a category in medical research is the focus of an intense debate, complicated by the inconsistency of presumed independent variables, race and ethnicity, on which analysis depends. Interpretation is made difficult by inconsistent methods for determining the race or ethnicity of a participant. The failure to specify how race or ethnicity was determined is common in the published literature.Hypothesis: Criteria by which they assign a research participant to racial or ethnic categories are not reported (...) by published articles.Methods: Methods were reviewed for assigning race and ethnicity of research participants in 268 published reports reporting associations among race , health outcome and genotype.Results: Of the 268 published reports reviewed, it was found that 192 did not explain their methods for assigning race or ethnicity as an independent variable. This was despite the fact that 180 of those reports reached conclusions about associations among genetics, health outcome and race or ethnicity.Conclusions: More attention needs to be given to the definition of race and ethnicity in genetic studies, especially in those diseases where health disparities are known to exist. (shrink)