Vulnerable populations, who have difficulty accessing the health care system, primarily receive their medical care from hospitals. Policy makers have struggled to ensure the survival of "safety-net hospitals," hospitals that provide a disproportionate share of care to these patient populations. The objective of this article is to develop measures to guide analysis and policy for urban safety-net hospitals. The authors developed three safety-net measures: the socioeconomic status of hospital service area, Medicaid intensity, and uncompensated care burden and its market share. Cluster analysis was used to identify break points that distinguish a safety-net hospital from a non-safety-net hospital. The measures developed were stable and independent, but a data-driven binary assignment of hospitals to a "safety-net" category was not supported. These analyses call into question the empirical basis for distinguishing a specific group of hospitals as safety-net hospitals.