In late 2002, colonoscopy was introduced as a primary screening tool for colorectal cancer (CRC) in Germany. We aimed to estimate the expected reduction in case numbers and incidence of CRC between 2003 and 2010 by detection and removal of advanced adenomas. Data from 1,875,708 women and men included in the national screening colonoscopy database were combined with estimates of transition rates of advanced adenomas and with national population projections. Despite relatively low screening participation, incident CRC cases are expected to be reduced by more than 15,000 between 2003 and 2010. The impact is expected to be largest in age groups 55-59, 60-64 and 65-69 in whom total case numbers in 2010 are expected to be reduced by 13%, 19% and 14% among women, and by 11%, 15% and 12%, respectively, among men. Our results forecast a major rapid reduction of the CRC burden in Germany by screening colonoscopy.