The National Cancer Policy Board and the Board on Science, Engineering, and Economic Policy convened a workshop in January 2004 on "Economic Models of Colorectal Cancer (CRC) Screening in Average-Risk Adults". The purpose of the workshop was to explore the reasons for differences among leading cost-effectiveness analysis (CEA) models of CRC screening, which public health policy makers increasingly rely on to help them sift through the many choices confronting them. Participants discussed the results of a collaborative pre-workshop exercise undertaken by five research teams that have developed and maintained comprehensive models of CRC screening in average-risk adults, to gain insight into each model''s structure and assumptions and possible explanations for differences in their published analyses. Workshop participants also examined the current state of knowledge on key inputs to the models with a view toward identifying areas where further research may be warranted. This document summarized the presentations and discussion at the workshop.