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A major health priority is to increase colorectal cancer screening, and colonoscopy has become an increasingly important method of screening. The Medicare program began coverage for colonoscopy for average risk individuals in 2001.We sought to examine whether overall colorectal cancer screening increased over time and whether these increases were a result of increased utilization of all methods or a result of greater use of colonoscopy but reduced use of other methods, whether the enactment of Medicare coverage was associated with an increase in colonoscopy among Medicare enrollees, and whether these trends equally affected subpopulations.We used nationally representative data from the 2000 and 2003 National Health Interview Surveys and analyzed data using used χ2, difference-in-differences tests, and logistic regression analyses to examine whether screening rates differed between 2000 and 2003.The percentage of individuals being screened for colorectal cancer using any method increased modestly from 2000 to 2003 (3%), with increases a result of increased use of colonoscopy and a reduction in the use of other methods. Increases in colonoscopy use were significant among all populations except the insured, non-Medicare population with low incomes. Among Medicare enrollees with high/middle incomes, colonoscopy use increased 14% from 2000 to 2003 compared with an increase of only 7% among low-income groups, which was a significant difference (P < 0.01). Similarly, among insured, non-Medicare enrollees with high/middle incomes, colonoscopy use increased 11% from 2000 to 2003 compared with an increase of only 4% among low-income groups, which also was a significant difference (P < 0.01).Colorectal cancer screening utilization increased modestly from 2000 to 2003, with the increases that primarily were the result of increased colonoscopy use. Increases in colonoscopy use, however, were primarily among high/middle income groups. Although Medicare coverage may have indirectly facilitated the increase in colonoscopy, we could not determine that coverage directly increased screening rates. Screening rates remain modest and lower income individuals continue to be screened less. Topics for future research include approaches to facilitating screening among low-income individuals and evaluating the impact of policy coverage decisions.