OBJECTIVES: Patient registries are important tools for health care research, but variations in definitions of outcome measures and their data elements make it difficult to compare or link data from different registries.  Standardizing outcome measures would help identify registries capturing similar information and promote collaboration, reduce redundancy, and improve efficiencies of new registries using standardized data elements.  The goal of this project, sponsored by the Agency for Healthcare Research and Quality (AHRQ), is to develop a prototype of an Outcome Measures Framework (OMF) for use within the Registry of Patient Registries (RoPR) to collate and characterize the outcome measures currently used in patient registries.  The long-term objective of the OMF is to support efforts to standardize outcome measures. METHODS: Stakeholders from a broad range of organizations (e.g., clinicians, registry sponsors, researchers, government agencies) were identified and invited to participate in a series of meetings to gather and refine the design requirements for the OMF.  Requirements were also refined through user acceptance testing.  Over 110 individuals participated in OMF design activities.  RESULTS: Stakeholders identified several challenges necessary to address in designing the OMF.  They want a framework that 1) distinguishes between outcome measures collected on a patient level and those collected or calculated on a population level; 2) describes the frequency or timeframe in which a particular outcome measure is collected; 3) identifies outcome measures that are clinically equivalent to each other and clearly displays this information; and 4) minimizes user burden, since participation in the RoPR is currently voluntary. CONCLUSIONS: By using a design process that solicited the opinions of a wide variety of stakeholders, several challenges were identified.  These challenges were addressed in the design of the OMF prototype, and will require further clarification if the OMF is developed and implemented into a system such as the RoPR.