Reauthorization of the Ryan White Comprehensive AIDS Resources Emergency Act requires that each jurisdiction estimate the number of people living with HIV/AIDS who have unmet need for care. Past assessments of unmet need have used various definitions of care, relied on qualitative evaluations, or examined nonrepresentative subpopulations. This article outlines a single, flexible framework designed to quantitatively estimate unmet need in varied settings. The framework adopts a definition of unmet need which focuses on HIV primary medical care (CD4 test, viral load test, or antiretroviral therapy in a 12-month period), employs a standard analytic structure to integrate population and care data, and allows use of locally available data. We report on three field tests (Louisiana, Atlanta, and San Francisco). The field tests suggest that the unmet need framework provides an approach which can be used by states and metropolitan areas to estimate the number of individuals with unmet need for HIV primary medical care.