Screening colonoscopy was introduced in Germany in October 2002. We aimed to quantify its effects on prevention, early detection, and overdiagnosis of colorectal cancer (CRC) in the 10 years since its introduction.

We analyzed data from more than 4.4 million screening colonoscopies (conducted on individuals 55–79 years old from 2003 through 2012) available through the national screening colonoscopy registry. CRCs prevented, detected earlier than they would have been without screening, and overdiagnosed (cancers detected at screening colonoscopy that would not have become clinically manifest during the patient’s lifetime) were estimated by Markov models. Model parameters included sex-specific and age-specific findings at screening colonoscopy; mortality; rates of transition from nonadvanced to advanced adenoma, advanced adenoma to preclinical cancer, or preclinical cancer to clinically manifest cancer; and protection from screening colonoscopy.

Overall, approximately 180,000 CRCs (1/28 screening colonoscopies) were estimated to have been prevented, and more than 40,000 CRCs (1/121 screening colonoscopies) were detected earlier than they would have been without screening, compared with approximately 4500 overdiagnoses (1/1089 screening colonoscopies). Almost all CRCs prevented or detected earlier than they would have been without screening resulted from screening colonoscopies performed on individuals up to 75 years old (97% and 89%, respectively), whereas 28% of overdiagnoses occurred from screening colonoscopies of individuals older than 75 years old.

On the basis of a 10-year analysis of data from a national registry in Germany, screening colonoscopies have large potential for prevention and early detection of CRC, with low risk of overdiagnosis.