The authors present the modern classification of colorectal polyps. They discuss the dysplastic and preneoplastic changes in the light of new data on predisposing factors. Although new techniques are developing such as immunocytochemistry, DNA cytophotometry, DNA recombination, it is clear that presently, the basic morphological data, microscopical as well as histological, retain an irreplaceable diagnostic value. From a practical point of view, the authors recall the importance of an adequate orientation of the polyps before their histological examination in order to obtain all the necessary informations permitting an accurate diagnosis: type of the polyp, possible areas of cancer formation and their depth of penetration, histology of the surrounding mucosa and tissues.