Objective. The Outcome Measures in Rheumatology (OMERACT) international consensus initiative has successfully developed core sets of outcome measures for trials of many rheumatologic conditions, but its expanding scope called for clarification and updating of its underlying conceptual framework and working process. To develop a core set of what we propose to call outcome measurement instruments, consensus must be reached both on what to measure and how to measure. This article deals with the first part: a framework necessary to ensure comprehensiveness of the domains chosen for measurement. We formulated a conceptual framework of core measurement areas in clinical trials, for discussion at the OMERACT 11 conference. Methods. We formulated a framework and definitions of key concepts adapted from the literature, and followed an iterative consensus process (small group processes and an Internet-based survey) of those involved including patients, health professionals, and methodologists within and outside rheumatology. Results. The draft framework comprises 4 core "areas": death, life impact (all aspects of how a patient feels or functions), resource use (monetary and other costs of the health condition and interventions), and pathophysiologic manifestations (disease-specific clinical and psychological signs, biomarkers, and potential surrogate outcome measures necessary to assess specific effects). The survey responses (262 of 2293, response rate 11%) indicated broad agreement with the draft framework and the proposed definitions of key concepts, including understandability and feasibility. A total of 283 comments were processed. Conclusion. In an iterative process, we have developed a generic framework for outcome measurement and working definitions of key concepts ready for discussion at the OMERACT 11 conference.