SYNOPSIS: No randomized, controlled trials of screening colonoscopy have been completed, and ongoing trials exclude persons aged 75 years or older. The Medicare program, however, reimburses screening colonoscopy without an upper age limit. We evaluated the effectiveness and safety of screening colonoscopy to prevent colorectal cancer (CRC) in persons aged 70 to 74 and those aged 75 to 79 years. We used observational data to emulate a target trial with 2 groups: colonoscopy screening and no screening. This talk will provide an overview of the motivation, implementation and methodological challenges faced in implementing this study.