Narrow band imaging represents a promising endoscopic technique which allows real time characterization of colonic lesions by assessment of mucosal and vascular patterns. Due to the ability to make an optical biopsy, NBI could become a useful tool in clinical decisions regarding therapy and surveillance. The aim of this paper is to review the current knowledge on the optical diagnosis of colonic lesions by using NBI endoscopy. We reviewed research articles, reviews and meta-analyses from the PubMed and MEDLINE containing relevant data in this field. The validity of endoscopic criteria for the differentiation of adenoma and hyperplastic polyps, as well as of invasive cancer, has been evaluated in recent studies. Based on the prediction of polyp histology, new potential cost saving strategies have been proposed. Many reports are focused on the accuracy of optical biopsy by using NBI for predicting colonoscopy surveillance intervals and adenomatous histology in diminutive polyps, according to the Preservation and Incorporation of Valuable Endoscopic Innovations statement. Optical diagnosis is still under evaluation, and cannot yet be endorsed in routine practice. The high level of performance achieved by expert endoscopists needs to be replicated in the community utilizing reliable and standardized endoscopic criteria.