Abstract Background: A growth of consensus and increasing activities related to organized cancer screening programs has occurred in Korea since 1999. It is important to assess disparities in the fight against cancer, and it is crucial to identify particular groups that may be experiencing a high burden of cancer-related illness. Methods: Data from 8,160 men and women ages >40 years from the 2005 to 2009 Korean National Cancer Screening Survey were used to analyze the relationship between socioeconomic position and receiving upper gastrointestinal series or upper endoscopy within the past 2 years. We used absolute and relative concentration indexes, that is, summary measures of disparity based on both rate differences and rate ratios. Results: For organized screening, the education disparity declined, but the income disparity index increased, indicating that participation in organized screening was relatively more concentrated among the lower-income groups. For opportunistic screening, income and education disparities increased due to the widening of socioeconomic differences. Conclusions: The results of this study suggested progress toward socioeconomic disparity-related goals in organized screening for gastric cancer. However, the income disparity trends in organized screening may change in a manner similar to those in opportunistic screening in the future because of the much faster rate of organized screening uptake by those higher on the socioeconomic scale. Impact: This study addresses the routine monitoring of coverage of screening among different socioeconomic groups and could be used to inform polices to reduce disparity in coverage. Cancer Epidemiol Biomarkers Prev; 19(8); 1919–26. ©2010 AACR.