The NICE classification is an international endoscopic classification of colorectal neoplasia through a narrowband spectrum that on the basis of lesion colors, vascular pattern, and structure of the surface of the mucous membrane classifies colorectal neoplasms in three categories: type 1 as hyperplastic lesions, type 2 as adenomas, and type 3 as invasive tumors. The aim of this study was to verify diagnostic accuracy of the NICE classification system compared to the reference standard: histopathological analysis. This retrospective study was conducted by ten physicians on a sequential sample of 418 patients and 735 polyps. The total diagnostic accuracy of the NICE classification system is found to be 76.7%. Optical recognition is significantly better with larger polyps, high-risk lesions (HGIEN), and neoplastic lesions. This research has shown that the NICE classification system is at the moment inferior to histopathological analysis. However, it is noticed that some physicians achieve significantly better results, with the accuracy of diagnosis ranging from 59.5% to 84.2%. These results show that with proper training of physicians and the use of endoscope enhancements to improve image quality, the NICE classification system could in the future potentially replace the histopathological diagnosis process.