In light of the racial-ethnic and poverty composition of the United States population and the distribution of syphilis morbidity across population subgroups, it is important to determine how race-ethnicity and poverty jointly and independently affect transmission dynamics of syphilis and other sexually transmitted diseases. Populations of minority race ethnicity and populations of poverty are both marked by youthful age composition and relative scarcity of men, and both populations live in areas of high poverty concentration. Sexually transmitted disease morbidity, particularly syphilis morbidity, is concentrated in these populations, which are neither purely racial-ethnic groupings nor purely economic groupings. This social context creates potential sex partner pools of high risk and high sexually transmitted disease prevalence, which carry a higher probability of exposure to infection for each sex act. The combined effects of poverty, minority race-ethnicity, and geographic clustering apparently contribute to persisting syphilis morbidity, particularly in the southeastern United States.