Health is unevenly distributed across socioeconomic status. Persons of lower income, education, or occupational status experience worse health and die earlier than do their better-off counterparts. This article discusses these disparities in the context of urban medical practice. The article begins with a discussion of the complex relationship among socioeconomic status, race, and health in the United States. It highlights the effects of institutional, individual, and internalized racism on the health of African Americans, including the insidious consequences of residential segregation and concentrated poverty. Next, the article reviews health disparities based on socioeconomic status across the life cycle, beginning in fetal health and ending with disparities among the elderly. Potential explanations for these socioeconomic-based disparities are addressed, including reverse causality (e.g., being poor causes lower socioeconomic status) and confounding by genetic factors. The article underscores social causation as the primary explanation for health disparities and highlights the cumulative effects of social disadvantage across stages of the life cycle and across environments (e.g., fetal, family, educational, occupational, and neighborhood). The article concludes with a discussion of the implications of health disparities for the practice of urban medicine, including the role that concentration of disadvantage plays among patients and practice sites and the need for quality improvement to mitigate these disparities.