Background: Aberrant crypt foci (ACF) have emerged as a putative precursor to colorectal adenoma, with potential use as a biomarker of colorectal cancer. However, there are wide differences in ACF prevalence, dysplasia, and histologic confirmation rates across studies. These differences may, in part, be because of variability in identification of endoscopic criteria. Objective: To systematically evaluate the accuracy and reliability of various endoscopic criteria used to identify ACF when using magnification chromoendoscopy (MCE). Design: Images obtained via MCE were shown to participating endoscopists who diagnosed them as ACF or not and who assessed them for the endoscopic characteristics used to identify ACF in the literature. Main Outcome Measurements: The predictive ability of the endoscopic criteria (crypt number, staining, margin, crypt size, epithelial thickness, and lumen shape) for histologic confirmation of ACF, and their reliability across endoscopists. The accuracy of the examiners in identifying ACF that were histologically confirmed was also assessed. Results: The interrater agreement rate for all except one of the endoscopic criteria (crypt number) was low and did not improve with training. None of the criteria could significantly predict histologic confirmation of ACF. Despite training exercises, accuracy of endoscopists to correctly identify a histologically proven ACF remained low. Limitations: Still images with ×40 optical magnification were analyzed rather than real-time endoscopy. All ACF samples were hyperplastic; none were dysplastic. Conclusions: No endoscopic criteria evaluated by our study predicted histologic confirmation of ACF. MCE had low accuracy and poor reliability.