To ensure that National Institutes of Health-funded research is relevant to the population's needs, specific emphasis on proportional representation of minority/sex groups into National Cancer Institute (NCI) cancer centers' clinical research programs is reported to the NCI. EMPaCT investigators at 5 regionally diverse comprehensive cancer centers compared data reported to the NCI for their most recent Cancer Center Support Grant competitive renewal to assess and compare the centers' catchment area designations, data definitions, data elements, collection processes, reporting, and performance regarding proportional representation of race/ethnicity and sex subsets. Cancer centers' catchment area definitions differed widely in terms of their cancer patient versus general population specificity, levels of specificity, and geographic coverage. Racial/ethnic categories were similar, yet were defined differently, across institutions. Patients' socioeconomic status and insurance status were inconsistently captured across the 5 centers. Catchment area definitions and the collection of patient-level demographic factors varied widely across the 5 comprehensive cancer centers. This challenged the assessment of success by cancer centers in accruing representative populations into the cancer research enterprise. Accrual of minorities was less than desired for at least 1 racial/ethnic subcategory at 4 of the 5 centers. Institutions should clearly and consistently declare their primary catchment area and the rationale and should report how race/ethnicity and sex are defined, determined, collected, and reported. More standardized, frequent, consistent collection, reporting, and review of these data are recommended, as is a commitment to collecting socioeconomic data, given that socioeconomic status is a primary driver of cancer disparities in the United States. © 2014 American Cancer Society.