Despite strong evidence for the effectiveness and cost-effectiveness of a variety of colorectal cancer (CRC) screening methods for reducing CRC mortality, current CRC screening rates fall far below the levels needed to significantly impact CRC mortality. Unfortunately, however, the existing literature on patient CRC screening behavior does not yet provide a sufficient evidence base for making sound recommendations regarding how to most effectively improve upon these rates in the VA. This study will inform future CRC screening promotion efforts and make important scientific contributions to existing literature by: (a) delineating the relative contribution of patient cognitive, environmental and background factors to CRC screening behavior using a multi-level, theory driven analysis approach on a nationally representative sample, and (b) identifying the determinants of variation in CRC screening behavior across vulnerable population subgroups.