Background: The racial disparity in outcomes for prostate cancer, gastric cancer, and multiple myeloma is demonstrated by these malignancies having the highest age-adjusted mortality rate ratio for black Americans versus white Americans. A variety of factors have been identified as contributing to this disparity, leading to our hypothesis that there would not be concordance, in respect to the mean, when the county-level age-adjusted black: white mortality rate ratio for a malignancy was compared to the other two malignancies. Methods: Publically available information from cancerrates.gov was used to obtain county-level data in regards to race-specific age-adjusted mortality rates for prostate cancer, gastric cancer, and multiple myeloma. Counties with potentially unstable age-adjusted mortality rates were excluded. A malignancy’s age-adjusted mortality rate for blacks was divided by the complementary rate for whites to determine the black: white mortality rate ratio. Across a county, malignancies were compared for concordance in mortality rate ratios relative to the mean ratio for that malignancy. After a preliminary inspection noted that all New Jersey counties had a markedly lower black: white mortality ratio for gastric cancer than other counties in the data set, the New Jersey counties were excluded from analysis and odds ratios for concordance were calculated. Results: All counties (n = 68) had a black: white age-adjusted mortality ratio of > 1 for each malignancy. In the analyzed counties (n = 52), there was a statistically significant concordance in black: white mortality rate ratios for prostate cancer and gastric cancer (OR = 3.26, p = 0.046). The black: white mortality rate ratios for neither prostate cancer (OR = 1.17, p = 0.78) nor gastric cancer (OR = 1.17, p = 0.78) demonstrated a statistically significant concordance with multiple myeloma. Conclusions: The concordance in the black: white mortality rate ratios for prostate cancer and gastric cancer in this dataset indicate that these two malignancies may share common clinical, environmental, or genetic factors in African-Americans. Future research is needed into what common factors may contribute to disparities in these two malignancies.