Large-bowel endoscopy with removal of polyps strongly reduces colorectal cancer risk. In epidemiologic studies, ascertainment of large-bowel endoscopies often relies on self-reports and might be prone to imperfect recall. In 2003-2004, the authors assessed the validity of self-reported colorectal endoscopies in a population-based case-control study including 540 cases and 614 controls from southwest Germany and calculated odds ratios of colorectal cancer risk according to self-reports and medical records. They sought to obtain all medical records for the last self-reported endoscopy and for a subsample of 100 subjects reporting no previous endoscopy. In total, 377 of 483 records could be obtained (78%). Sensitivity of self-reports was 100%, and specificity ranged from 93% to 98% among subgroups defined by age, gender, education, family history of colorectal cancer, and case-control status. The odds ratios for colorectal cancer risk after previous colonoscopy were 0.31 (95% confidence interval: 0.21, 0.45) using self-reports and 0.31 (95% confidence interval: 0.20, 0.47) using medical records. However, agreement between self-reports and medical records was poor regarding type of endoscopy (colonoscopy, sigmoidoscopy, or rectoscopy; kappa = 0.22), moderate concerning polypectomy (kappa = 0.58), and reasonable for year of examination (kappa = 0.70). Self-reports of previous colorectal endoscopies agreed well with medical records, but validation appears to be essential with respect to details of the examination.