The goal of this project is to present a two-day national conference on "Diagnostic Error in Medicine - 2009". The ultimate goal of this meeting is to improve patient safety by reducing the likelihood of diagnostic error in medicine. Diagnostic errors comprise a significant fraction of medical errors and are responsible for substantial harm and avoidable healthcare costs. Addressing the problem of diagnostic error relates to AHRQ's major focus on the quality of medical care and to many AHRQ priorities, including the focus areas of patient safety, medical error, ambulatory care, and the use of informatics to improve the quality of medical care. This conference will be held Oct 21-22, 2009 in Los Angeles, California in conjunction with (and just following) the annual meeting of the Society for Medical Decision Making (SMDM). This plan will capitalize on the common interests of attendees at these two meetings and allow for joint registrations, sharing common expenses, and using key faculty at both conferences. The inaugural conference "Diagnostic Error in Medicine - 2008" was held in May of 2008 and attracted 125 participants from 6 countries. The proposal for this second conference will build on progress started at the first conference, and expand on the major themes in this area. The conference content will include both academic (Day 1 - Understanding Diagnostic Error) and practical sessions (Day 2 - Reducing Diagnostic Error). Day 1 sessions will cover the evolving understanding of clinical reasoning and the cognitive origins of diagnostic error, and Day 2 events will focus on real-world options and experience with reducing diagnostic error, including decision-support tools and organizational approaches to error reduction. Abstract sessions will be devoted to presenting the results of ongoing research projects. A major goal of the conference is to continue work on defining agenda for research and education in this field, building on the work initiated at the inaugural conference in 2008. Speakers will be internationally recognized leaders in this new field, including both researchers and clinicians from diverse disciplines. The patient's and provider's perspective will be included from speakers with personal involvement in diagnostic error.